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V6-K 

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No.  161.  ISSUED   MAY,  1903.  Vol. 


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X     -^  .JWDEXEO 


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'^  JOURNAL 


OF  THE 


INSTITUTION  OF 

ELECTBIOAL   ENGINEEBS, 

LATB 

W  SOCIETY  OF  TELE6I(APH-EH6IHEERS  AND  ELECTKICIANS. 

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Vol.  32.  1903. 


139913R 


ASTOR.  LENOX  AND 
FOlWUAiiONS 
1941  L 


ff^    T<^T 


The  Three  Hundred  and  Eighty-ninth  Ordinary  General 
Meeting  of  the  Institution  was  held  at  the  Institution 
of  Civil  Engineers,  Great  George  Street,  Westminster, 
on  Thursday  evening,  February  26th,  1903 — Mr.  James 
Swinburne,  President,  in  the  chair. 

The  minutes  of  the  Ordinary  General  Meeting  of  February  12th 
were,  by  permission  of  the  meeting,  taken  as  read,  and  signed  by  the 
President. 

The  names  of  new  candidates  for  election  into  the  Institution  were 
also  taken  as  read,  and  it  was  ordered  that  these  names  should  be 
suspended  in  the  Library. 

The  following  list  of  transfers  was  published  as  having  been 
approved  by  the  Council  : — 

From  the  class  of  Associate  Members  to  that  of  Members — 

Sydney  Evershed.  I       W.  F.  Stuart-Mcnteth. 

Edgar  Llewellyn  Ingram.  |       Laurence  Maxwell  Waterhouse. 

From  the  class  of  Associates  to  that  of  Members — 

Frederick  William  Topping. 

From  the  class  of  Associates  to  that  of  Associate  Members — 


Arnold  Grant  Livesay. 
William  Marsh. 
Francis  Samuel  Miller. 
Alexander  Houston  Weddell. 


George  Ernest  Etlinger. 
Archibald  Ernest  Grant. 
Arthur  Frederick  Harris. 
Leopold  J.  Harris. 

From  the  class  of  Students  to  that  of  Associates — 

Samuel  Blackley.  |       Sydney  Elliott  Glendenning. 

Mahmoud  Samy. 

Messrs.  W.  R.  T.  Cottrell  and  W.  Nairn  were  appointed  scrutineers 
of  the  ballot  for  new  members. 

Donations  were  announced  as  having  been  received  since  the  last 
meeting  to  the  Library  from  the  Maschinenfabrik  Oerlikon,  and  the 
Relatives  of  the  late  A.  T.  Weightman  ;   to  the  Building  Fund  from 

Vol.  82.  85 


4^ 

620      ^  STOTTNER:  THE  NERNST  LAMP.  '        [Feb.  a6th, 

Messrs.  A.  Eden,  F.  Heppenstall,  H.  W.  Lee,  A.  P.  Pyne,  R.  C.  Quin, 
D.  C.  Wardlaw,  L.  Wilson;  and  to  the  Benevolent  Fund  from 
J.  W.  Fletcher,  J.  G.  Wilson,  and  J.  H.  Woolliscroft,  to  whom  the 
thanks  of  the  meeting  were  duly  accorded. 

The  President  :  Mr.  W.  R.  Cooper,  who  has  been  the  Institution's 
representative  on  the  Committee  of  Science  Abstracts^  has  been  elected 
Secretary  of  the  Physical  Society,  and  therefore  he  can  no  longer 
represent  this  Institution.  Mr.  Kingsbury  has  kindly  consented  to 
take  his  place,  but  the  Council  particularly  instructed  me  to  mention 
this  matter  to  the  meeting,  because  we  feel  that  the  Institution  is  very 
much  indebted  to  Mr.  Cooper  for  the  immense  amount  of  hard  work 
he  has  done  as  editor  in  past  days,  and  the  work  he  has  most  recently 
done  as  the  most  active  member  of  the  Committee. 

At  the  last  meeting  I  reminded  members  of  the  Institution  that  the 
Council  would  be  glad  to  receive  any  suggestions  of  names  for  the 
candidature  of  the  new  Council.  As  I  then  explained,  the  Council  do 
not  bind  themselves  in  any  way  to  nominate  people  so  recommended, 
but  they  will  be  very  glad  of  any  names  suggested  by  members,  and 
they  will  be  carefully  considered. 

I  will  now  ask  Mr.  J.  Stottner  to  read  the  paper  in  his  name  on  the 
Nernst  Lamp.  ^ 

*N^  THE   NERNST   LAMP. 

By  J.  Stottner,  Member. 

Few  inventions  in  electrical  science  have  created  greater  expecta- 
tions, excitement,  and  speculation  than  the  Nef nst  Lamp,  and  with  few 
have  there  been  such  immense  difficulties  in  obtaining  practical  and 
satisfactory  results. 

From  the  time  of  the  earliest  application  of  the  Edison  glow-lamp 
attempts  were  made,  first,  to  discover  a  substitute  for  the  carbon 
filament ;  secondly,  to  avoid  the  necessity  of  evacuating  and  sealing 
the  globe ;  and  thirdly,  in  case  of  the  filament  giving  out,  to  accomplish 
its  exchange  without  at  the  same  time  throwing  away  the  body  of  the 
lamp  itself. 

In  1877  Jablochkoff  took  out  a  patent  for  a  lamp  in  which  the 
illuminating  body  consisted  of  kaolin  and  similar  refractory  earths, 
which  become  conductors  of  electric  current  as  soon  as  heated  to  a 
certain  temperature. 

Partly  on  account  of  the  very  low  efficiency,  but  more  particularly 
by  reason  of  the  necessity  for  very  high-tension  currents,  this  invention 
— in  common  with  all  other  attempts — proved  a  failure,  until  Professor 
Walther  Nernst  came  to  the  front  with  his  lamp  in  the  year  1898. 

I  have  lately  visited  the  extensive  lamp  works  of  the  Allgemeine 
Elektricitats-Gesellschaft,  and  will  endeavour  to  make  you  acquainted 
with  the  development  of  the  Nernst  lamp  manufactured  there  from  its 
earliest  stage  up  to  its  present  design,  for  which  purpose  the  A. E.G. 
has  bc#n  kind  enough  to  supply  me  with  original  samples  of  the  lamp 


1908.]  STOTTNER:  THE  NERNST   LAMP.  621 

in  its  various  stages  of  development  and  design.  The  filaments  of  all 
these  lamps  are  made  of  rare  earths,  principally  of  zirconia. 

The  earlier  types  of  Nernst  lamps  had  no  automatic  heating  arrange- 
ment, and  the  filament  or  glower,  as  our  cousins  in  America  call  it,  had 
to  be  heated  to  the  temperature  required  (on  an  average  about  700"  C.) 
to  make  it  a  conductor,  by  means  of  a  spirit  lamp  or  match. 

The  very  first  lamp  brought  out  was  type  No.  i  (Plate  I.)  with  a 
straight  filament,  the  compensating  resistance  (or  bolstering  resistance  as 
it  is  termed  on  the  Continent)  of  which,  consisting  of  a  fine  platinum  wire, 
^was  arranged  in  parallel  with  the  filament  at  a  distance  of  about  ^  in. 

In  t3rpe  No.  ia  (Plate  I.)  the  filament  was  bent  in  a  similar  manner  to 
that  of  the  first  Edison  bamboo  carbon  incandescent  lamp,  and  was  in 
the  shape  of  a  horseshoe.  The  burner  of  this  lamp  could  be  exchanged. 

The  bulb  was  open  in  order  to  facilitate  artificial  heating  of  the 
filament,  as  mentioned  before.  The  bolstering  resistance,  to  which  I 
shall  refer  again  later,  consisted  of  fine  platinum  wire  wound  round 
two  small  porcelain  tubes,  and  was  exposed  to  the  air  to  obtain  a  better 
cooling  effect. 

The  filament  in  t3rpe  No.  2  (Plate  I.)  was  exactly  the  same  as  in 
No.  IA,  but  the  bolstering  resistance  was  wound  on  one  small  porcelain 
tube  only,  and  partly  covered  with  kaolin. 

In  type  No.  3  (Plate  I.)  the  resistance  consisted  of  thin  iron  wire  wound 
on  a  very  small  kaolin  tube,  which  was  sealed  and  enclosed  in  a<glass  tube. 
This  tube  was  evacuated  and  afterwards  filled  with  hydrogen  gas.  All 
these  models,  however,  proved  unsatisfactory,  and  platinum  wire  was 
again  resorted  to  as  a  bolstering  resistance,  as  type  No.  4  (Plate  I.)  shows. 

In  this  lamp  the  large  loop  is  the  resistance,  which  was  prepared  in 
almost  exactly  the  same  manner  as  the  heater  of  the  present  day,  a 
very  fine  platinum  wire  being  wound  in  a  spiral  on  a  thin  kaolin  tube 
and  then  steeped  in  a  solution  containing  kaolin.  The  small  loop  is  the 
filament.  It  will  be  noticed  that  in  this  lamp  filament  and  resistance 
are  fixed  for  the  first  time  on  a  porcelain  base.  This  shape  of  resistance 
was  in  use  for  a  considerable  time  and  will  be  seen  again  in  the  later  types. 

The  trouble  of  lighting  the  lamps  by  means  of  a  spirit  lamp  or  match, 
however,  prevented  their  being  brought  into  general  use.  They  were 
exhibited  for  the  first  time  in  public  in  conjunction  with  some  auto- 
matically-heated lamps  at  the  Paris  Exhibition  of  1900,  where  the 
patentees,  the  Allgemeine  Elcktricitats-Gesellschaft,  of  Berlin,  had  a 
magnificent  pavilion  lighted  entirely  by  Nernst  lamps.  At  this  time 
the  difficulties  had  by  no  means  been  overcome,  but  seemed  rather 
only  to  have  commenced,  and  it  was  found  absolutely  necessary  to 
cfiEect  the  heating  of  the  filament  automatically  in  order  to  bring  the 
lamp  into  practical  use. 

In  type  No.  5  (Plate  I.)  the  automatic  heater  will  be  observed  for  the 
first  time.  The  filament  in  this  type  was  again  a  straight  rod,  placed 
horizontally  to  the  base  of  the  lamp.  The  thick  porcelain  tube  next  to 
it  contained  the  heating  wire,  and  the  smaller  tube  the  bolstering 
resistance.  Both  filament  and  bolstering  resistance  in  this  lamp  could 
be  exchanged.  The  automatic  cut-out  was  embedded  in  the  socket. 
It  will  be  observed  that  the  magnet  had  great  masses  of  iron  and  a 


522  STOTTNEK:  THE   NERNST   LAMP.  [Feb.  26th, 

heavy  armature,  in  consequence  of  which  a  ;»reat  deal  of  energy  was 
required  to  actuate  it. 

In  type  No.  6  (Plate  I.)  we  see  for  the  first  time  a  heater  in  the  form 
of  a  coil,  in  the  centre  of  which  the  filament  is  placed.  The  heating  coil 
was  prepared  in  a  similar  manner  to  that  in  type  No.  4,  but  mounted 
together  with  the  filament  on  a  somewhat  larger  base,  and  could  be 
easily  exchanged.  The  bolstering  resistance  was  the  same  as  in  type 
No.  3  and  could  be  exchanged,  but  was  firmly  fixed  to  the  socket. 
The  magnet  was  identical  with  that  of  type  No.  5,  and  the  glass  bulb 
similar  to  that  of  an  ordinary  incandescent  lamp. 

Type  No.  7  (Plate  I.)  is  very  similar  to  No.  6.  This  lamp  was 
designed  for  220  volts.  The  filament  could  not  be  arranged  in  a 
horizontal  position  on  account  of  its  length,  and  therefore  both  filament 
and  heater  were  mounted  vertically  to  the  base. 

A  great  improvement  is  shown  in  type  No.  8  (Plate  I.).  Here  for 
the  first  time  will  be  observed  in  the  bolstering  resistance  spirals  of 
thin  iron  wire  suspended  free  of  the  carrier. 

Type  No.  9  (Plate  II.)  was  a  departure  from  the  usual  practice,  in 
which  a  loop  filament  was  again  used  and  a  magnetic  cut-out  placed 
alongside  of  the  bolstering  resistance  instead  of  being  embedded  in  the 
socket. 

Up  to  this  time  the  lamps  had  been  manufactured  only  in  small 
numbers,  but  types  Nos.  10,  11,  12  (Plate  II.)  and  13  (Plate  III.)  were 
now  designed  and  for  the  first  time  produced  in  considerable  quantities. 
These  lamps  show  two  distinct  forms,  the  *'  A  "  type  with  large  body 
and  globe,  and  the  "B"  type  with  small  round  globe  and  body  so 
ananged  that  it  could  be  used  in  an  ordinary  Ekiison  screw  lamp  socket. 

The  "  B "  lamps,  types  10  and  1 1  were  manufactured  for  an  energy 
consumption  of  40  and  80  watts  and  potentials  of  no  and  220  volts 
respectively.  The  bolstering  resistance  in  these  types  again  consisted 
of  platinum  wire  as  in  type  No.  4.  As  on  account  of  their  small  size 
it  was  impossible  to  combine  these  filaments  with  a  modern  iron 
resistance  they  were  all  arranged  in  a  horizontal  position.  The  heating 
spirals  were  mounted  firmly  on  the  porcelain  baseplate,  which  could  be 
easily  exchanged.  In  these  lamps  the  magnet  of  the  automatic  cut-out 
received  its  final  shape,  being  marked  by  very  small  masses  of  iron 
and  a  very  light  spring,  and  in  consequence  thereof  by  a  very  small  loss 
of  energy.  The  **  A  "  lamps  were  for  higher  currents  up  to  i  ampere, 
and  had  to  be  separately  connected  in  a  similar  manner  to  that  in 
which  an  arc  lamp  is  connected. 

Types  12  and  13  were  designed  for  an  energy  consumption  of 
100  and  200  watts  with  a  corresponding  lighting  capacity  of  65  and 
130  standard  candle-power  respectively.  In  this  type  the  burner,  as 
well  as  the  bolstering  resistance,  could  be  independently  exchanged. 
These  lamps  were  made  for  no  and  220  volts.  As  opposed  to  the 
"  B "  lamp,  the  filament  and  the  heating  coil  were  arranged  in  a 
vertical  position.  The  design  of  the  magnets  of  the  automati^JuTouts 
was  exactly  the  same  as  that  in  the  "  B  "  lamps.  'rjMrmetal  cap 
covering  the  resistance  was  provided  with  ventilatin^jjflots,  so  that  the 
bolstering  resistance  was  cooled  by  the  circulation^ 


I 


(Showing  Kemsl  Lainj\  Types  s-8} 


Plate  II. 
(Showing  Nernst  Lamp,  Types  9-12,  and  24.) 


Plate  III. 
(Showing  Nernst  Lamp,  Types  13  and  25.) 


VAhh\hh.hhH\\hh%\SShVAHHVA\hMJ^WAfJ 


1903.]  STOTTNER:  THE   NERNST   LAMP.  523 

Types  Nos.  14,  15,  16,  17  and  17A  show  the  development  of  the 
Nernst  lamp  as  a  candle  lamp  for  chandeliers,  etc.  These  lamps  do 
not  deviate  materially  from  those  described  up  to  now,  but  correspond 
with  the  ordinary  lamps  in  each  successive  stage  of  development. 

In  Nos.  18,  19  and  20,  the  gradual  reduction  of  the  iron  masses 
in  the  magnet  will  be  noticed.  The  first  magnet  weighs  about  three 
times  as  much  as  those  in  use  at  the  present  day. 

Nos.  21,  22  and  23  (Plate  III.)  show  experiments  in  disconnecting 
the  heater  by  other  means  than  that  of  an  electromagnetic  cut-out. 

Sketches  A,  B  and  C  (Plate  IV.) show  the  corresponding  diagrams  of 
current  in  these  devices.  The  springs  of  compound  metal  bend  to  one 
side  as  soon  as  heated.  These  inventions,  however,  did  not  come  into 
practical  use  and,  indeed,  never  left  the  laboratory.  I  merely  mention 
them  to  show  that  all  kinds  of  researches  wxre  made  with  the  object  of 
improving  the  details  of  Nernst  lamps. 

Nos.  24  (Plate  II.)  and  25  (Plate  III.)  show  the  latest  patterns  of 
Nernst  lamps,  as  now  in  use  by  the  million. 

No.  24  is  the  A  type  lamp.  The  burners  are  manufactured  for 
I  ampere  up  to  250  volts,  and  for  i  ampere,  only,  from  200  up  to  250 
volts.  The  metal  hood  is  furnished  with  metal  combs  of  thin  sheet 
copper  in  the  inner  cover,  for  the  purpose  of  cooling  the  bolstering 
resistance.  Between  this  inner  tube  and  the  outer  mantle  are  a  number 
of  tubes  for  ventilation  purposes  and  to  facilitate  the  radiation  of  heat. 

The  replacing  and  fixing  of  burners  is  a  very  simple  manipulation, 
and  can  be  effected  by  any  unskilled  person. 

For  customers  who  have  A  lamps  of  the  old  type  we  have  designed 
special  adapters,  so  that  the  new  burners  can  be  used  on  such  lamps. 

No.  25  (Plate  III.)  is  the  latest  B  type  lamp,  which  is  manufactured 
for  i  and  i  ampere  up  to  150  volts,  and  for  J  ampere  up  to  250  volts. 

The  replacement,  etc.,  of  burners  is  quite  as  simple  as  in  the  case 
of  the  A  type  lamp. 

Nos.  26  to  36  are  various  bolstering  resistances,  all  made  of  iron 
wire,  sealed  in  glass  globes  which  have  been  evacuated  and  afterwards 
filled  with  hydrogen.  Iron  wire  is  used  on  account  of  its  high 
temperature  correction,  which  makes  it  particularly  suitable,  as,  for 
instance,  should  the  current  increase  5  per  cent,  the  resistance  of  the 
iron  wire  increases  about  75  per  cent.,  thus  preventing  the  destruction 
of  the  filament.  The  increase  of  resistance  in  the  iron  wire  is  not 
proportionate  throughout,  and  it  is  therefore  necessary  that  the  sectional 
area  should  be  chosen  with  a  view  to  heating  the  wire  to  a  critical 
temperature  by  the  current  with  which  the  lamp  is  intended  to  burn, 
in  order  to  arrive  at  the  above-mentioned  result,  i.e.,  the  balancing 
of  current  by  resistance. 

Nos.  37  and  38  show  filaments  which  have  burned  1,400  and  1,600 
hours  respectively.  Unfortunately  No.  37  is  broken,  but  from  No.  38  it 
can  be  easily  seen  that  the  filament  has  become  crystallised.  It  is  also 
black  throughout ;  this  discoloration  starts  at  the  negative  pole  and 
gradually  extends  over  the  whole  filament.  The  precise  cause  of  this 
crystallisation  and  blackening  is  not  at  present  known,  but  we  presume 
that  it  is  due  to  electrolysis. 


524  STOTTNER:  THE  NERNST  LAMP.  [Feb.  26th, 

As  to  the  efficiency  and  life  of  the  Nernst  lamp,  I  refer  to  the  table 
of  tests  made  at  the  Physikalische  Technische  Reich  sanstalt  at 
Charlottenburg. 

A  number  of  lamps  have  been  under  test  at  the  Electrical  Testing 
and  Standardising  Institution  at  Faraday  House,  London,  since  the 
middle  of  December.    The  results,  however,  are  still  outstanding. 

A  great  many  errors  in  the  treatment  of  Nernst  lamps  are  committed, 
in  consequence  whereof  numerous  complaints  of  short  life,  etc.,  are 
lodged  with  the  suppliers ;  but  if  instructions  are  carefully  followed  a 
life  of  about  300  to  400  hours — ^as  practical  results  show — may  be 
expected.  One  great  mistake  generally  made  is  that  the  current  is  sent 
through  the  lamps  in  the  opposite  direction  to  that  intended,  particularly 
in  the  "  B  *'  type  lamp.  Another  mistake  is  to  overrun  the  lamps,  as 
the  surplus  current  is  then  taken  up  by  the  bolstering  resistance  and 
practically  the  light  is  not  in  the  least  increased. 

On  the  Continent  the  screw  holder  is  in  almost  universal  use,  and 
the  standard  rule  is  to  make  the  centre  contact  minus  ;  it  is  therefore 
immaterial  how  frequently  the  lamps  are  taken  out  of  their  holders,  as 
they  always  come  back  to  their  proper  position.  With  bayonet  lamps 
it  is  different :  the  poles  can  be  easily  changed  by  inserting  the  lamps 
the  wrong  way,  and  to  prevent  this  the  A.  E.G.  have  designed  a  tool 
to  cut  out  a  slot,  and  have  provided  the  porcelain  socket  of  the  lamp 
with  a  third  pin,  so  that  it  is  impossible  to  get  the  lamps  into  the 
holders  the  wrong  way. 

To  determine  the  polarity  on  bayonet  sockets  special  pole-finders 
are  supplied,  the  negative  pole  being  invariably  indicated  by  the  red 
appearance  of  the  solution. 

I  have  studied  the  principles  and  designs  of  the  Nernst  lamps 
manufactured  in  the  United  States,  and  think  that  we  here  in  the  Old 
World  may  pride  ourselves  on  being  at  least  as  up-to-date  as  our 
American  cousins. 

Mr.  Drake.  Mr.  B.  M.  DRAKE :  We  are  indebted  to  Mr.  Stottner  for  kindly 

giving  us  the  history  of  the  evolution  of  the  Nernst  Lamp,  as  wd^-ked 
out  by  the  Allgemeine  Elektricitats-Gesellschaft,  of  BerHn,  and  it  may 
be  of  interest  to  compare  what  has  been  going  on  in  this  country  in 
connection  with  the  same  problem.  As  you  may  know,  when  this 
invention  was  first  brought  to  public  notice,  attempts  were  made  at 
a  meeting  at  Berlin  of  the  holders  of  all  the  patents  of  Nernst  for  the 
world  to  arrange  for  an  interchange  of  experience  by  which  the  lamp 
might  be  brought  to  perfection  in  less  time  than  would  be  possible  if 
each  worked  on  his  own  account.  At  that  meeting,  which  Mr. 
Swinburne  and  I  attended  on  behalf  of  the  Nernst  Electric  Light 
Company,  there  were  present  Mr.  Westinghouse,  the  AUgemeine 
Elektricitats-Gesellschaft,  and  Messrs.  Ganz.  Two  days  were  spent  in 
discussing  the  invention,  which  was  regarded  as  marking  a  new  era. 
There  was  a  serious  discussion  as  to  the  result  on  the  electrical  industry 
when  the  lamp  should  make  its  appearance.  One  influential  member 
said  there  was  no  doubt  that  if  these  lamps  were  put  upon  the  market 
indiscriminately  the  supply  companies'  business  throughout  the  world 


1908.] 


THE  NERNST  LAMP:  DISCUSSION. 


525 


would  be  affected  to  a  serious  extent :  the  companies  would  suddenly  Mr.  Drake, 
find  that  their  output  was  halved,  with  the  result  that  it  would  be 
impossible  for  them  to  pay  dividends  for  the  year.  It  was  further 
stated  that  it  would  be  impossible  for  the  wiring  contractors,  however 
numerous  they  might  be,  to  wire  the  additional  houses  which  would  at 
once  rush  for  the  electric  light,  owing  to  the  fact  that  the  cost  of 
lighting  would  be  halved.  All  sorts  of  methods  were  suggested  as  to 
how  the  lamp  should  be  put  upon  the  market  gradually,  so  as  not  to 
upset  the  electrical  industry.  These  hours  of  discussion,  however, 
were  somewhat  wasted,  for  providence  looked  after  the  electrical 
industry.  As  soon  as  we  had  finished  our  discussion,  we  all  went  home 
and  discovered  that  none  of  us  could  make  the  lamp  at  all.  Un- 
fortunately, owing  to  international  jealousy,  we  were  unable  to  come 
to  any  arrangement  by  which  we  could  arrange  an  interchange  of 
improvements,  and  the  result  was  that  each  tried  to  work  out  the  lamp 
for  himself.  There  are  on  the  table  specimens  showing  the  progress 
of  the  Nernst  lamp  as  we  designed  it  in  England.  Unfortunately  we 
had  not  the  unbounded  resources  of  the  AUgemeine  Elektricitiits- 
Gesellschaf t,  and  we  were  blessed  with  a  boisterous  set  of  shareholders, 
who  would  not  leave  us  alone,  besides  which  we  had  to  manufacture 
out  of  England.  Had  it  not  been  for  these  drawbacks  I  think  we 
should  have  put  our  lamp  on  the  market  as  soon  as,  if  not  sooner  than, 
the  AUgemeine  Elektricitkts-Gesellschaft.  Some  of  the  results  which 
we  were  able  to  produce  are  shown  in  the  curves  exhibited.  These 
are  the  mean  results  of  a  number  of  tests  which  were  made  ;  and  you 
will  see  from  the  Curve  Fig.  A  that  we  were  able  to  produce  lamps  which 


r 

<3 


20 


10 


too       £00     JOO 


400      500       600       TOO 
Life  in  Hours 

Fig.  a. 


&00      900    IjOOO 


started  at  20  candle-power,  and  after  800  hours  had  only  dropped  to 
16*5.  The  tests  were  very  carefully  taken,  and  will  compare  favourably 
with  the  results  obtained  by  any  carbon  lamp  which  has  ever  been 
made  :  the  average  watts  being  27  per  candle  throughout  the  whole 
period.  The  next  diagram  (Fig.  B)  shows  the  drop  in  candle- 
power  of  large  lamps  of  200  volts,  starting  at  130  candle-power  and 
ending  at  about  80,  with  a  mean  efficiency  of  2*3  watts  in  700  hours. 


526 

Mr.  Drake.  i^q 

K 

\ 

<e 

i  60 

I 


STOTTNER  :  THE  NERXST  LAMP.  [Feb,  26th, 


\, 

'^ 

— . 

-^ 

too 


zoo 


300  ^900 

Life   in    Hours 

Fig.  B. 


500 


600 


700 


the  Curve  Fig.  C  shows  the  rapid  way  in  which  the  volts  absorbed 
by  the  resistance  increase  with  the  smallest  increase  of  current.  The 
result  is  that  when  these  series  resistances  are  used  with  Nernst  lamps 

you  get  a  more  regular  candle- 
power  with  variations  of  volt- 
age than  with  the  carbon  lamp. 
The  Curve  Fig.  D  shows  the 
percentage  variation  of  candle- 
power  of  the  carbon  lamp  and 
the  Nernst  lamp,  with  different 
voltages.  It  will  be  seen  from 
this  that  in  the  Nernst  lamp 
the  candle-power  does  not  in- 
crease to  anything  like  the 
same  extent  as  in  the  carbon 
lamp.  The  carbon  lamp,  with 
a  rise  from  loo  to  115  volts, 
has  increased  in  candle-power 
in  a  ratio  of  100  to  230, 
whereas  the  Nernst  lamp  under 
the  same  increase  of  pressure 
has  only  increased  to  130.  The 
iron  resistance  may  be  looked 
upon  as  one  of  the  turning 
points  in  the  Nernst  lamp,  and 
it  will  be  used  to  advantage 
in  series  with  the  ordinary 
carbon  lamp  on  traction  cir- 
cuits where  the  voltage  is  not 
very  regular.  In  Mr.  Stottner's 
paper  there  are  one  or  two 
points,  probably  slips,  to  which  perhaps  he  will  not  mind  my  referring. 
Near  the  top  of  page  521  he  talks  of  the  resistance  being  arranged 
in  parallel  with  the  61ament ;  I  think  he  means  in  series. 


o-e 


o^      06     o-e 

Current  in  Amperes 
Fig.  C. 


10       IE 


1903.] 


THE   NERNST   LAMP:  DISCUSSION. 


627 


Mr.  Stottxer  :  As  a  matter  of  fact  the  resistance  and  filament  are   Mr. 
arranged  in  parallel,  but  electrically,  of  course,  they  are  connected  in  ^'*^""*''- 
series. 

Mr.  Drake  :  The  next  point  is  with  regard  to  the  claim  of  the  Mr.  Drake. 
Allgemeine  Elektricitats-Gesellschaft  to  be  the  first  to  show  an 
automatic  lamp.  Mr.  Swinburne  will  bear  me  out  that  the  lamp 
originally  shown  at  the  Society  of  Arts,  which  is  on  the  table,  is 
automatic,  the  heating  hood  being  lifted  by  a  powerful  magnet  away 
from  the  glower.  Also  automatic  lamps  made  by  Ganz  were  shown 
in  1899,  at  the  Royal  Society.  The  Ganz  lamps  are  also  on  the  table 
for  the  inspection  of  members  who  would  like  to  see  them.  The  lamps 
whicli  are  alight  now  are 
some  of  the  products  of  *3^or 
the  Ncrnst  Company.  I 
would  ask  Mr.  Stottner 
to  look  at  one  of  them 
with  duplex  glowers,  be- 
cause the  Allgemeine 
Elektricitats-Gesellschaft 
might  do  well  to  adopt 
it.  We  have  not  seen  any 
of  their  make  arranged 
in  this  way,  and  for  street 
lighting  they  are  very 
suitable  because  a  single 
glower  hardly  gives 
enough  light!  for  street 
purposes,  whereas  the 
two  just  suffice.  The 
Westinghouse  Company 
have  not  up  to  the  pre- 
sent produced  a  con- 
tinuous-current lamp,  Mr. 
Westinghouse  having 
concentrated  his  attention 
on  the  alternating  lamps, 
and,  curiously  enough, 
we  found  the  alternating 

a  much  more  difficult  problem  than  the  continuous.  The  Westing- 
house lamps,  which  are  also  on  the  table,  consist  of  a  large  number 
of  small  glowers;  I  presume  he  found  difficulty  in  baking  the 
large  glowers,  which  is  a  difficult  problem,  and  required  a  consider- 
able time  to  solve.  Mr.  Westinghouse  fuses  the  conductors  into  the 
ends  of  his  glowers  in  a  way  which  is  different  fropi  that  adopted  by 
others,  which  is  apparently  better  for  alternating  glowers.  Messrs. 
Ganz  started  very  energetically  on  the  Nernst  lamp,  and  the  specimens 
shown  on  the  table  are  very  creditable  examples,  considering  the 
time  at  which  they  were  made.  But  as  soon  as  they  found  the 
enormous  outlay  which  would  be  necessary  in  order  to  bring  the 
Nernst  lamp  into  a  practical  state,  they  apparently  got  frightened  and 


3£>         100         loa        110         //5 
PercenCoLge  of  Normal  L  f^iMSure 

Fig.  D. 


628  STOTTNER:  THE  NERNST  LAMP.  [Feb.  26th, 

Mr.  Drake.  yqH  it  alone  altogether.  We,  for  commercial  and  company  reasons, 
have  made  arrangements  with  the  Allgemeine  to  manufacture  for  our 
districts,  and  therefore  the  Allgemeine  must  be  gii^en  the  full  credit  for 
being  the  first  in  the  world  to  put  the  Nernst  electric  lamp  on  the 
market  in  a  condition  in  which  it  will  meet  commercial  requirements. 

Hammond.  ^^*  ^'  Hammoxd  :   I  was  hoping  that  the  general   body  of  the 

members  would  take  the  opportunity  presented  to  them  of  having 
these  leading  experts  on  the  Nernst  lamp  in  the  same  room  with  them, 
to  do  a  little  heckling.  And  I  am  surprised  at  the  backwardness 
of  those  who,  I  am  sure,  have  so  many  questions  to  ask.  Possibly, 
however,  they  will  come  on  a  little  later  in  the  evening.  With  regard  to 
my  attitude  towards  the  lamp — and  I  think  possibly  it  is  the  attitude  of 
most  of  us — I  feel  that  the  ideas  which  were  prevalent  originally  that  the 
.  introduction  of  a  lamp  of  very  much  higher  efficiency  would  greatly 
damage  our  industry,  arc  absolutely  chimerical.  The  more  cheaply  we 
can  utilise  the  energy  which  we  produce,  the  more  cheaply  we  can 
give  light,  and  the  more  important  will  our  industry  grow.  I  had  the 
pleasure  of  visiting  the  Buffalo  Exhibition,  and  I  was  very  much  struck 
with  the  splendid  exhibit  of  George  Westinghouse  ;  I  spent  more  time 
in  that  portion  of  the  exhibition  than  in  any  other  portion,  and  I  came 
back  to  England  feeling  that  there  was  no  reason  why  we  should  not 
start  in  this  country  street-lighting  by  means  of  Nernst  lamps.  Now, 
I  am  much  interested,  as  I  am  sure  you  all  must  be,  to  hear  from 
Mr.  Stottner  that  the  whole  question  of  the  efficiency  and  life  of  the 
lamp  has  been  settled  by  the  tests  made  at  the  Physikalische  Tech- 
nische  Reichsanstalt  of  Charlottenburg.  You  tell  that  to  a  town 
councillor,  and  unless  he  can  get  his  friends  to  vote  him  a  sufficient 
sum  to  go  and  visit  these  works  himself,  he  wants  the  efficiency 
demonstrated  on  the  spot.  I  therefore  undertook  for  my  friends  and 
paymasters  at  Hackney  to  carry  out  a  mile  of  street  lighting  on  the 
Nernst  system  ;  and  I  was  anxious  to  do  so,  not  that  I  disregarded  the 
wonderful  results  that  were  achieved  by  the  Physikalische  Technische 
Reichsanstalt  of  Charlottenburg,  but  because  I  felt  that  if  the  Nernst 
lamp  was  going  to  supersede  the  old-fashioned  lighting  which  prevails 
in  the  streets  of  the  United  Kingdom,  it  would  do  so  after  practical 
results  in  the  streets,  rather  than  in  the  laboratory  of  the  Physikalische 
Technische  Reichsanstalt,  that  very  excellent  institution  at  Charlotten- 
burg. Now,  we  have  got  a  mile  of  street  lighted,  and  in  due  course  I 
was  called  upon,  in  conjunction  with  the  resident  electrical  engineer, 
Mr.  L.  L.  Robinson,  to  give  a  report  as  to  the  extension  of  the  lighting 
to  the  whole  of  the  125  miles  of  streets  in  Hackney.  Well,  of  course, 
as  a  consulting  engineer  always  anxious  to  extend  the  scope  of  one's 
work,  I  was  naturally  tempted  to  say.  Go  in  and  light  the  whole  mileage. 
But  with  due  regard  to  a  character  which  it  is  so  difficult  in  these  days 
to  keep,  I  felt  that  it  would  be  well  that  I  should  lay  before  the 
councillors  of  Hackney  some  actual  results.  And  I,  knowing  their 
attitude,  did  not  drown  them  with  those  achieved  by  the  Physikalische 
Technische  Reichsanstalt  of  Charlottenburg.  I  had  to  tell  them  how 
much  per  annum  each  lamp  was  likely  to  cost  them  on  the  basis  of  the 
life — or  want  of  life,  because  you  cannot  tell  the  length  of  life  until  it 


1908.]  THE  NERNST  LAMP :  DISCUSSION.  529 

is  dead — of  those  that  had  already  been  put  up.  You  see,  gentlemen,  Mr 
how  far  removed  from  science  one  sometimes  has  to  be.  And  finally 
I  laid  before  them  this  report.  It  is  not  all  Physikalische  Technische 
Reichsanstalt ;  there  are  one  or  two  other  things  in  it,  and  I  shall  have 
very  much  pleasure  in  presenting  it  to  the  Institjition,  which  will  be 
even  a  greater  pleasure  than  reading  it  all  through  to  you  to-night.  So 
that  if  it  be  deemed  worthy,  or  if  any  portion  of  it  be  deemed  worthy 
by  the  Editing  Committee  to  constitute  a  sort  of  supplement  to  the 
scientific  contribution  that  has  been  so  ably  made  to-night,  it  is  at  the 
disposal  of  that  Committee.  But  what  I  found  was  this  : — First,  that 
of  these  lamps,  which  were  placed  roughly  about  42, 43, 45  yards  apart, 
40  lamps  going  to  the  mile,  the  first  one  finished  his  life  in  130  hours. 
The  cause  of  this  failure  was  failure  of  flex  connected  to  the  glower. 
Now  I  am  sure  you  will  all  agree  with  me  that  having  a  gentleman 
before  us  who  is  so  well  acquainted  with  the  reason  of  flexes  failing, 
he  will  be  able  to  give  us  some  idea  of  how  we  shall  be  able  to  arrange 
that  in  future  the  flexes  connected  with  the  glower  do  not  fail.  I  may 
say  that  by  the  commercial  arrangement  which  has  been  referred  to  by 
Mr.  Drake,  all  the  lamps  were  obtained  from  the  Electrical  Company, 
and  it  is  therefore  for  Mr.  Stottner  to  tell  us  why  in  No.  i  lamp,  which 
we  thought  was  going  to  last  so  efficiently  for  800  hours,  the  flex  failed 
in  130  hours.  We  had,  of  course,  to  fix  another  lamp  in  its  place,  and 
the  second  lamp,  up  to  the  time  of  the  making  of  these  tests,  lasted  930 
hours,  and  he  is  going  on  lasting.  With  regard  to  the  No.  2  lamp  in 
the  street,  it  was  going  merrily  on  after  542  hours.  No.  3  lamp  had  to 
have  a  good  deal  of  attention  paid  to  it  We  had  men  carefully 
patrolling  this  mile  the  whole  time,  so  as  to  be  able  to  get  accurate 
results.  The  first  lamp  fixed  on  No.  3  post  disappeared  in  34  hours 
because  there  was  a  fracture  of  the  glower  at  bottom  contact ;  and 
that  is  the  constant  fault  we  have  discovered,  at  all  events  at  Hackney. 
This  report,  I  may  say,  is  dated  February  2nd  of  this  year.  The 
second  lamp  fixed  on  No.  3  post  gave  a  life  of  96  hours,  and  in  that, 
again,  there  was  fracture  of  glower  at  bottom  contact.  The  third 
lamp  put  in  there  lasted  453  hours,  and  died  from  failure  of  heating- 
coil  due  to  faulty  action  of  auto-cutout.  We  put  in  a  fourth,  and  that 
disappeared  in  150  hours  ;  he  went  back  to  the  old  complaint,  and,  like 
his  grandfather  and  his  greatgrandfather  before  him,  he  died  from 
fracture  of  glower  at  bottom  contact.  And  the  fifth  lamp  took  up  the 
running,  and  at  the  time  of  the  test  was  241  hours  old.  I  am  not  going 
to  weary  you  by  reading  the  history  of  the  whole  of  them,  but  the 
awkward  thing  is  this,  that  the  lives  vary  considerably.  It  reminds  you 
of  a  chapter  in  Genesis,  because  some  of  them  lived  to  such  an 
advanced  age ;  thej'  vary  from  1,070  hours  and  still  young,  to  15  hours 
and  dead  and  gone.  And  the  15-hour  one  died  from  failure  of  the 
heating  coil.  We  put  another  one  in  his  place,  who  only  attained 
a  life  of  30  hours,  and  he  died  from  failure  of  the  heating-coil.  Well 
now,  these  figures,  which  I  think  you  may  take  as  absolutely  reliable, 
can  be  summarised  as  follows.  The  total  number  of  burners  tested  to 
full  life  was  67.  The  total  burner  hours,  including  only  such  burners 
as  failed,  was  20,499  >  ^^®  average  life  of  the  burners,  that  is  to  say  the 


Hammond. 


530 


STOTTNER  :  THE  NERNST  LAMP. 


[Feb.  26th, 


Mr. 
Hammond. 


Professor 
Ayrton. 


dead  ones  (as  we  cannot  get  their  average  lives  till  they  die),  was  305 
hours.  Taking  that  as  the  basis  of  the  life,  I  was  compelled  to  get 
these  results  out  in  advising  as  to  whether  I  could  conscientiously 
recommend  the  Vestry  to  permit  me  to  light  the  whole  125  miles  of 
streets  by  this  means.  We  found  that  these  lamps  gave  their  80 
candle-power  pretty  consistently  with  the  half  an  ampere  on  a  240- volt 
circuit.  I  will  take  the  working  cost  of  3,940  hours  per  annum, 
debiting  the  current  at  l}d. — as  a  matter  of  fact  it  was  I'yd. — debiting 
them  with  renewals  on  the  basis  of  the  life  shown  by  these  experiments, 
11*5  burners  and  one  resistance  and  one  globe,  sundry  stores  and 
labour.  We  thus  get  a  certain  net  cost  of  working.  The  lanips  then 
have  to  be  debited  with  the  interest  on  the  repayment  of  capital  on  the 
basis  of  a  ten  years'  loan  at  3^  per  cent,  plus  8J  per  cent.,  equals  12  per 
cent.,  a  total  sum  of  £^  17s.  9d.  per  annum.  Well  now,  in  this  country 
the  town  councillors  [of  course  not  the  ekctrical  engineers  (nothing  in 
the  way  of  electricity  is  too  dear  to  them),  who  may  consider  that 
£$  17s.  9d.  would  be  a  very  proper  expenditure  per  lamp  for  the  sake 
of  having  the  Nernst  lamp]  think  that  that  figure  does  not  compare 
favourably  with  the  price  which  would  hold  at  all  events  if  the  lamps 
lasted  as  long  as  they  do  at  Charlottenburg.  I  think  we  may  ask  Mr. 
Stottner  to  help  us  in  his  reply  to  explain  the  causes  of  these  failures, 
because,  speaking  for  myself  as  representing  Hackney,  I  should  be 
only  too  delighted  if  these  failures  did  not  occur,  and  if  the  whole  of 
those  125  miles  of  streets  were  lighted  with  that  lamp.  And  I  think 
that  what  applies  to  Hackney  applies  also  through  the  country.  We 
cannot  do  with  a  lamp  that  has  not  a  uniform  life.  In  the  early  days 
of  the  incandescent  lamp,  as  we  recollect,  and  our  President  will 
remember  one  or  two  episodes  with  regard  to  it,  the  difficulty  was  not 
that  of  making  the  lamp — our  President  made  them  in  large  quantities 
— but  the  difficulty  was  that  of  getting  them  uniform.  If  you  attempt 
to  put  in  lamps  for  street  lighting  some  of  which  last  15  hours,  and 
some  of  which  last  1,000  hours,  it  puzzles  even  a  consulting  engineer, 
electrical  as  he  may  be,  or  otherwise,  to  determine  the  proper  number 
of  renewals  which  he  has  to  provide  for ;  because  you  cannot  have 
street  lighting  with  certain  lamps  out  and  certain  lamps  in.  The  disin- 
clination to  push  the  Nernst  lamp  throughout  the  country  is,  I  think, 
largely  due  to  its  not  being  a  truth-teller  ;  he  does  not  always  do  what 
his  brother  did  yesterday.  If  we  can  get  all  the  members  of  the  family 
to  live  the  same  life,  even  if  it  is  not  800  hours,  but  790,  or  665,  we 
shall  have  attained  very  much  nearer  to  its  adoption  than  we  have  got 
to-day. 

Professor  W.  E.  Ayrton,  F.R.S.  :  I  will  only  say  one  word,  as  it  is 
getting  very  late.  I  want  to  ask  one  question.  Mr.  Hammond  has 
dealt  in  a  very  facetious  way  with  the  attempt  to  light  a  street  in 
Hackney  with  the  Nernst  lamp  ;  but  the  point  I  wish  to  "deal  with  is 
the  one  which  Mr.  Hammond  has  passed  over  so  easily.  He  has  only 
dealt  with  failure  arising  from  mechanical  causes.  No  doubt  those  are 
very  serious  for  any  practical  system  of  lighting,  but  with  improved 
manufacture  those  failures  can  be  overcome.  But  what  I  want  to  deal 
with  is  the  point  which  he  passed  over,  namely,  that  these  lamps  do 


1903.]  THE   NERNST   LAMP:  DISCUSSION.  631 

give  the  8o-candle-power  light  during  the  whole  of  their  life.     Now,   Professor 
my  experience  has  been  the  opposite.    It  is  a  small  experience,  I  grant  "' 

as  far  as  lamps  that  I  have  used  myself  is>*  concerned,  but  it  is  not  a 
small  one  if  one  looks  at  the  Nernst  lamps  in  shops  and  various  other 
places.  And  I  would  like  to  ask  one  of  the  numerous  experts  whom 
"we  have  the  pleasure  of  seeing  here  to-night  on  the  subject  of  this 
Nernst  lamp,  why  the  practical  Nernst  lamp  does  not  follow  any  such 
curve  as  shown  in  those  diagrams.  If  the  English  Company  were  able 
some  time  ago,  as  I  understood  Mr.  Drake  to  say,  to  make  Nernst 
lamps  which  in  800  hours  only  fell  from  19  candles  to  16*5,  why  is  it 
that  such  lamps  are  not  made  and  sold  at  the  present  day  ?  One  other 
question  is,  what  is  the  cause  of  the  falling  off  of  the  light  of  a  Nernst 
lamp  ?  I  should  like  to  know  that  very  much.  One  knows  that  in  the 
case  of  the  ordinary  glow  lamp  it  is  due  to  a  change  in  the  surface  of 
the  carbon  filaments,  by  which  it  becomes  a  worse  radiator  of  light, 
and  sends  off  the  energy  at  a  lower  temperature.  Does  anything  like 
that  occur  to  some  extent  on  the  Nernst  filament  ?  Does  its  surface 
change  so  that  as  it  ages,  say  after  100  or  200  hours,  it  gives  off  energy  at 
a  lower  temperature  ?  Or  what  is  it  that  happens  ?  Is  it  a  change  in 
its  nature  which  causes  what  must  be  the  common  experience  of  many 
present,  namely,  the  light  to  fail  and  not  to  remain,  as  I  wish  it  did, 
f  oDowing  the  curve  such  as  Mr.  Drake  has  indicated  ? 

Mr.  M.  Solomon  :  I  should  like  to  add  a  few  remarks  to  what  has  Mr. 
already  been  said  on  the  Nernst  lamp,  especially  with  reference  to 
Professor  Ayrton's  comments  on  the  candle-power  cur\xs  shown  by 
Mr.  Drake.  Of  course  one  does  not  always  get  such  good  results  as 
these,  especially  so  good  as  those  in  the  curve  in  Fig.  A,  which  repre- 
sents the  mean  result  of  tests  on  three  lamps.  That  curve  does  drop  a 
certain  amount,  and  the  curve  in  Fig.  B  drops  rather  more,  but  perhaps 
the  average  curve  obtained  with  the  commercial  lamp  of  to-day  drops 
more  than  either.  Still  I  would  point  out  one  fact  with  reference  to 
judging  the  performance  of  the  lamps  by  those  which  one  sees  burning 
in  shops,  namely  that  in  the  first  part  of  the  curve  there  is  a  very 
marked  drop  in  candle-power  from  about  130  to  no.  My  experience 
is  that  there  is  always  a  drop  corresponding  to  that,  though  not 
perhaps  always  so  great,  and  sometimes  a  little  greater.  The  result  is 
that  after  the  first  50  hours  the  light  from  a  Nernst  lamp  seems  to 
change  a  good  deal  in  colour  on  account  of  this  first  drop.  The  light 
is  a  very  white  one  at  first  and  remains  white  during  the  whole  life, 
but  one  notices  a  considerable  difference  in  shade  if  two  lamps,  one 
new  and  one  50  hours  old,  are  observed  side  by  side.  But  after  that 
drop  the  candle-power  remains  fairly  steady,  as  shown  by  the  curve, 
which  is  quite  a  typical  one.  When  the  curve  drops  off  sharply 
towards  the  end  it  is  a  sign  that  the  lamp  is  about  to  fail. 

It  is  interesting  to  note  in  connection  with  the  curves  in  Figs.  C  and 
D  showing  the  behaviour  of  the  iron  resistance  and  the  increase  of 
candle-power  with  increase  of  voltage,  that  one  may  actually  lose  in 
efficiency  by  over-running  a  Nernst  lamp.  The  reason  is  obvious  when 
you  think  of  it,  for  if  the  lamp  is  over-run  by  15  per  cent,  the  candle- 
power  is  only  increased  very  slightly,   but  the  volts  taken   by  the 


682 


STOTTNER  :  THE  NERNST  LAMP. 


tFeb.  26th, 


Mr. 

Solomon. 


resistance  are  increased  by  a  very  great  amount.  The  result  is  that 
the  percentage  of  the  total  volts,  and  therefore  the  percentage  of  the 
total  watts,  absorbed  by  the*  resistance  is  very  much  greater,  and  the 
actual  over-all  efficiency  of  the  lamp  I  have  found  usually  falls  when 
the  potential  di£Ference  at  the  terminals  is  increased.  This  is  clearly 
shown  by  the  curves  in  Fig.  E,  which  are  for  a  half -ampere  200- volt 
Nernst  lamp.  It  will  be  noticed  that  the  total  watts  per  candle  increase 
slightly  when  the  supply  pressure  is  raised  above  the  normal.  There- 
fore it  is  of  course  not  only  inadvisable  but  useless  to  try  to  get  more 
out  of  a  Nernst  lamp  by  over-running  it.  The  curves  for  the  iron 
resistance  have  already  been  referred  to  by  Mr.  Drake,  and  also  by  Mr. 
Swinburne  in  his  presidential  address ;  they  are  very  remarkable 
curves,  and  the  Nernst  lamp,  by  leading  to  the  invention  of  this  iron 
resistance,  has  given  us  what  is  in  some  ways  a  new  piece  of  electrical 
apparatus,  which  may  be  of  great  use  in  other  classes  of  work.    One 


ISO 


I90  200  aio  2Z0  e30 

/bCenC/ciC    Difference  At  Lcunp  dermindiis  in  VoUs 
Fig.  E. 


can,  for  example,  use  these  resistances  in  series  with  an  arc,  and  one 
can  get  certain  results  by  so  doing  which  it  is  very  difficult  to  obtain  in 
other  ways.  If  a  resistance  of  this  sort  is  used  it  is  possible  to  run  an 
arc  with  a  very  low  current  more  steadily,  and  on  a  circuit  of  lower 
voltage  than  is  possible  with  an  ordinary  resistance.  I  have  tried  this 
experiment,  and  succeeded  to  a  certain  extent,  though  there  are  certain 
difficulties  in  the  way.  The  explanation  is  clear  if  one  considers  the 
curves  for  the  arc  which  were  first  published  by  M.  Blondel,  and  which 
Mrs.  Ayrton  has  made  familiar  to  us  all.  The  resistances  can  also  be 
used  with  ordinary  glow  lamps,  and  it  might  be  a  great  advantage  to 
use  them  with  the  standard  incandescent  lamp  described  by  Professor 
Fleming.  It  would  do  away  with  the  objection  which  must  militate 
against  the  use  of  a  carbon  lamp  as  a  standard,  namely,  that  the  candle- 
power  is  so  sensitive  to  the  voltage  ;  by  using  a  resistance  of  this  sort 
one  gets  a  curve  similar  to  that  for  the  Nernst  lamp  in  Fig.  D,  and  one 


1908.] 


THE   NERNST  LAMP :  DISCUSSION. 


688 


Solomon. 


Mr. 

Vignoles. 


can  get  much  better  working  results  for  practical  purposes  in  this  way  Mr. 
and  can  dispense  with  the  trouble  of  having  to  use  a  potentiometer.  °"**"* 

I  should  like  to  refer  to  one  other  matter.  Mr.  Drake  called  your 
attention  to  the  two-glower  lamp  which  is  shown  on  the  table  :  there  is 
also  exhibited  another  two-glower  lamp  in  which  the  glowers  are 
arranged  in  series,  so  that  it  runs  direct  on  a  400-  or  500-volt  circuit. 
This  lamp  has  been  run  and  tested,  and  it  worked  extremely 
satisfactorily  on  a  500-volt  circuit. 

Professor  Ayrton  :  Will  Mr.  Solomon  add,  to  the  interesting  in-  Professor 
formation  he  has  given,  one  fact  ?  The  lower  curve  is  of  such  ^y^""- 
enormous  importance  that  I  wish  to  ask  this  question.  It  is  a  ciu-ve 
showing  that  under  some  conditions  the  Nernst  lamps  are  as  good 
as  far  as  their  life  is  concerned,  as  a  very  good  ordinary  carbon  glow 
lamp,  but  giving  a  higher  efficiency.  I  want  to  ask,  did  you  require 
much  more  heating  to  make  that  particular  Nernst  filament  glow? 
Did  you  expend  much  more  power  in  your  heating  coil  than  you  do 
with  an  ordinary  commercial  lamp  so  as  to  start  the  glowing  of  the 
filaments  which  were  used  in  those  six  lamps  ? 

Mr.  Solomon  :  In  answer  to  Professor  Ayrton,  I  may  say  that  those  Mr. 
lamps  were  perfectly  ordinary  Nernst  lamps,  and  had  exactly  the  same 
heating  coil  as  the  commercial  lamps  which  the  Nernst  Electric  Light, 
Ltd.,  were  then  making.    This  coil  took  practically  the  same  current 
as  the  modern  commercial  lamp  made  by  the  A.E.G. 

Mr.  E.  B.  Vignoles  :  I  want  to  ask  one  question  with  regard  to  a 
point  which  has  not  yet  been  touched  upon  this  evening.  It  has  regard 
to  the  liability  to  damage  due  to  variations  in  the  voltage  on  the  lamp 
terminals.  With  the  instructions  which  the  Allgemeine  Elektricitats- 
Gesellschaft  send  out  with  their  lamps  is  a  statement  to  the  effect  that 
the  voltage  on  the  lamps  must  be  kept  steady.  My  experience  of  these 
lamps  is  limited,  but  I  have  found  that  with  the  ordinary,  more  or  less 
unsteady,  voltage  which  is  provided  in  my  factory  for  the  purposes  of 
lighting  the  lamps  gave  out  in  a  very  short  time.  Will  Mr.  Stottner 
tell  us  to  what  extent  the  voltage  may  be  allowed  to  vary  with  impunity, 
and  whether  the  rapidity  of  variation  in  the  voltage  has  any  effect  on 
the  lamps  or  their  resistances  ?  For  instance,  if  I  put  the  lamp  on  to  a 
dynamo  driven  by  a  gas  engine  which  is  varying  frequently  to  the 
extent  of,  say,  5  per  cent,  of  its  voltage,  is  the  lamp  likely  to  give  out 
quickly?  It  would  appear  from  the  breakdowns  to  which  I  call 
attention  that  the  fine  iron  wire  is  run  at  such  a  temperature  that  quite 
moderate  variations  of  voltage  are  sufficient  to  destroy  it :  and  this 
defect  seems  serious,  in  view  of  the  fact  that  on  any  supply  a  temporary 
rise  of  voltage  is  liable  to  occur. 

Mr.  A.  A.  C.  SwiNTON  :  Another  point  with  regard  to  which  I  think 
it  would  be  desirable  to  have  further  information  is,  the  comparative 
results  that  can  be  obtained  with  these  lamps  with  continuous  currents, 
and  with  alternating  currents.  Personally,  I  have  had  a  satisfactory 
experience  of  their  working  with  continuous  currents  in  my  office. 
But  in  other  places  where  I  have  had  them  tried  and  the  current  is 
alternating,  with  a  frequency  of  80,  the  results  have  not  been  good  at 
all.     Now,  what  I  am  anxious  to  know  is  this :  Is  this  difference  in 


Mr. 

Swintofi. 


534  SfOTTNER:  THE   NERNST   LAMP.  [Feb.  26th, 

swinton.        result  due  to  something  inherent  in  the  alternating  current,  or  is  it  due 
to  what  I   think  may  possibly  have   been   the  fact,  that  with   the 
alternating  current  the  voltage  was  not  quite  as  steady  ?     I  have  my 
office  in    Victoria    Street,  and   I   am  supplied  by  the  Westminster 
Company,  whose  voltage  is  exceedingly  steady,  but  I  rather  fancy  that 
there  is  something  in  alternating  current  which  does  not  agree  with 
these  lamps.    That  is  only  surmise  on  my  part,  however.    With  regard 
to  the  falling  off  of  the  candle-power,  the  scientific  aspect  of  the 
question  has  been  mentioned  by  Professor  Ayrton.     Now  the  filaments 
of  these  lamps  are  made  of  materials  the  same  as,  or  analogous  to,  those 
used  for  incandescent  gas  mantles  ;  and  it  is  well  known  to  everybody 
who  uses  incandescent  gas  mantles  that  these  mantles  fall  off  very 
much  in  candle-power  in  course  of  time.     I  think  the  reason  they  fall 
off  is  also  known.     I  believe  I  am  right  in  saying  that  the  Welsbach 
mixture  of  which  these  mantles  arc  composed  is  about  99  per  cent,  of 
oxide  of  thorium  and  i  per  cent,  of  oxide  of  cerium,  and  it  makes  an 
enormous  difference  what  the  exact  proportion  of  cerium  is ;  i  per 
cent,  makes  all  the  difference  in  the  world.     I  understand   that  the 
cerium  is  more  volatile  than  the  thorium,  and  that  consequently  after 
a  time  the  cerium  has  a  tendency  to  disappear.     In  fact,  I  believe  that 
the  ordinary  practice  of  the  manufacturers  of  incandescent  gas  mantles 
is  to  put  in  too  much  cerium  to  begin  with,  so  that  really  you  get  the 
best  effect  at  about  the  middle  of  the  life  of  the  mantle.    At  first  sight 
one  might  think  that  a  similar  effect  may  be  the  reason  for  the  falling  off 
in  the  candle-powder  of  these  Nernst  lamps,  but  I  wish  to  put  forward 
a  reason  which  I  think  makes  that  exceedingly  doubtful.    About  two 
or  three  years  ago  I  made  some  experiments,  which  were  communicated 
to  the  Royal  Society,  upon  the  luminosity  of  incandescent  mantles  ;  the 
mantles  were  not  exactly  like  those  made  for  ordinary  use,  but  were 
made  very  thick,  though  manufactured  in  the  same  way.  I  heated  them 
to  bright  incandescence  by  bombarding  them  with  cathode  rays  in  a 
vacuum  tube  ;  and  I  found  that  whereas  in  a   Bunsen  gas  burner  a 
mantle  of  purt  oxide  of  thorium  gives  only  something  like  one-eleventh 
of  the  light  that  is  got  with  a  mantle  made  of  the  Welsbach  mixture, 
pure  oxide  of  thorium  when  bombarded  with  cathode  rays  gave  practi- 
cally the  same  amount  of  light  as  the  Welsbach  mixture.    There  was  a 
slight  difference,  but  the  difference  was  estimated  at  not  more  than  5  per 
cent.     Wc  had  a  patchwork  mantle  made,  half  of  one  and  half  of  the 
other,  and  when  we  bombarded  it  equally  all   over  we  could  barely 
see  that  one  half  was  brighter  than  the  other.    That  goes  against  the 
theory  of  evaporation  and  consequent  alteration  in  the  mixture  being 
the  cause  of  the  falling  off  in  the  light  when  the  heating  is  effected  by 
anything  else  than  a  gas  flame,  and  I  am  inclined  to  suggest  that  it  is 
probably  a  change  in  resistance  more  than  anything  else  that  causes 
the  Hght  to  diminish ;  that  the  electrical  efficiency  remains  more  or 
less  the  same,  but  that  the  current  goes  down,  and  with  it  the  light. 
I  think  this  is  a  most  interesting  subject,  and  I  have  a  great  belief 
in  the  future  of  these  lamps  provided  that,  as  I  have  no  doubt  is  the 
case,  the  defects  mentioned  by  Mr.  Hammond  can  be  got  over  by 
improved  manufacture.   Further,  I  think  that  this  question  of  improved 


1903.] 


THE   NERNST   LAMP:    DISCUSSION. 


585 


lamps  is  one  of  the  most  important  subjects  which  can  be  discussed  by   Mr. 
this  Institution.  ^'^°*°°- 

Sir  Henry  Mange  :  With  reference  to  the  inquiry  as  to  the  amount  Mance°'^ 
of  current  taken  to  warm  up  the  heater,  I  may  say  I  have  tested  these 
lamps  for  some  thousands  of  hours  at  my  private  residence,  and  have 
found  that  the  heating  current  was  rather  more  than  that  which  the 
lamp  took  after  the  heater  was  cut  out  of  circuit.  With  regard  to 
suitability  for  alternating  currents,  my  house  is  connected  to  the  mains 
of  the  Brompton  and  Kensington  Company,  which  supplies  alternating 
current  at  loo  volts,  the  pressure  being  extremely  regular.  I  daresay 
I  have  tried  at  least  20  or  30  of  these  lamps ;  I  have  found  their  life 
varied  from  150  up  to  800  hours.  One  of  the  causes  of  failure,  as 
already  stated  by  Mr.  Hammond,  was  that  the  lead  up  to  the  glower 
failed  just  at  the  point  of  contact ;  and  I  made  the  suggestion  that  the 
contact  should  be  arranged  in  the  form  of  a  ring,  so  that  if  the  lower 
portion  of  the  ring  gave  way  there  would  be  still  remaining  the  upper 
portion  of  it,  and  the  life  of  the  lamp  would  be  thereby  prolonged.  I 
noted  the  current  which  all  these  lamps  took  very  carefully,  and  I  think 
the  statements  which  have  been  made  by  the  inventor  and  those 
interested  in  the  exploitation  of  the  Nernst  lamp  have  been  fully  borne 
out.  As  chairman  of  a  company  which  supplies  electric  current,  you 
might  perhaps  think  I  am  afraid  of  the  effect  that  the  lamp  might  have 
on  our  revenue.  But  I  myself  welcome  anything  which  will  cheapen 
and  popularise  the  use  of  the  electric  light.  There  is  no  doubt  that 
the  lamp  takes  one  half  the  current  of  the  present  lamps,  but  1  think 
that  long  before  the  conservative  British  public  have  taken  to  the  use 
of  the  Nernst  lamp  they  will  have  been  educated  up  to  requiring  twice 
the  amount  of  light. 

There  is  one  rather  important  point  which  perhaps  the  author  might 
assure  us  about,  and  that  is,  how  the  lamp  stands  transport  ?  I  made 
some  experiments  myself  with  the  replacement  pieces  in  the  earlier 
days,  when  the  lamp  was  nothing  like  so  perfect  as  it  is  now.  The 
results  of  these  experiments  were  not  altogether  satisfactory.  This  is  a 
most  important  point,  as  the  lamps  have  to  be  despatched  to  the 
furthest  corners  of  the  world. 

Mr.  Drake  :  I  would  like  to  answer  Professor  Ayrton's  question. 
The  bottom  curve  was  taken  with  lamps  which  started  with  about  2 
watts  per  candle,  instead  of  17.  Everybody  tried  to  make  the  Nernst 
lamp  do  more  than  it  could  do ;  and  we  made  experiments  to  see 
if  it  would  not  be  better  in  the  end  if  we  started  at  2  watts,  rather 
than  17  which  gave  such  a  rapid  drop  in  candle-power.  We  certainly 
got  a  better  result  than  is  obtained  from  the  lamps  which  are  now 
being  put  on  the  market. 

The  President  :  We  have  had  this  evening  a  very  interesting 
discussion.  We  have  had  Mr.  Stottner,  who  represents  the  German 
manufacturers  of  this  new  industry  ;  and  then  we  have  had  Mr.  Drake, 
who  not  only  represents  the  English  Company,  but  is  really  more  than 
an  ordinary  Director,  for  he  has  done  an  immense  amount  of  the  actual 
detail  work  himself  with  the  Nernst  Company.  And  we  have  had 
Mr.  Solomon,  who,  with  Mr.  Sheppard,  has  also  done  a  great  deal  of 

Vol.  32.  86 


Mr.  Drake. 


The 
President. 


636  STOTTNER:   THE  NERNST  LAMP.  [Feb.  26th, 

PrKidcnt  Original  work.  I  wish  we  could  have  had  something  from  Mr.  Sheppard 
too.  We  have  not  heard  anjrthing  from  the  Ganz  people  on  the 
subject,  and  we  have  not  a  representative  here  from  the  Westinghouse 
Company  to  tell  us  what  is  going  on  abroad.  Before  calling  on 
Mr.  Stottner,  I  would  like  to  say,  partly  in  reply  to  Professor  Ayrton, 
that  the  manufacture  of  these  filaments  is  exceedingly  difficult,  not 
only  as  a  matter  of  ordinary  manufacture,  but  as  a  matter  of  very 
intricate  chemistry.  One  reason  why  the  English  Company,  though 
they  did  not  make  many  filaments  and  lamps,  got,  in  some  cases, 
particularly  good  results,  was  the  enormous  care  they  took  over  the 
chemical  preparation.  Any  one  who  is  familiar  with  the  chemistry  of 
the  rare  earths  knows  it  is  exceedingly  difficult  to  purify  many  of  them. 
Some  of  them  can  only  be  purified  by  continual  re-crystallising.  And 
in  any  case  the  purification  of  zirconia,  which  is  one  of  the  chief 
components,  is  very  difficult.  As  to  the  other  part  of  the  filament,  it 
is  really  a  group  of  earths.  You  can  buy  "yttria"  from  a  manufacturing 
chemist,  but  you  can  never  guarantee  that  any  two  bottles  contain  the 
same  substance.  They  are  mixtures  of  the  same  group  of  oxides,  and 
it  is  very  difficult  to  know  exactly  what  you  are  getting.  First,  there 
is  the  mechanical  question,  and  then  there  is  the  chemical  question. 
It  is  apparently,  exceedingly  important  to  get  the  material  out  of  which 
the  filament  is  made,  in  a  given  physical  condition,  especially  to  get  it 
sufficiently  fine.  A  slight  difference  in  this  way  made  a  great  difference 
in  the  life  and  the  change  of  resistance  of  the  filaments. 

As  to  why  a  lamp  should  go  down  in  life  when,  apparently,  it  is 
controlled  by  a  resistance  which  will  practically  keep  the  watts  in  it 
constant,  or  nearly  constant,  that  raises  a  very  interesting  question. 
I  do  not  want  to  contradict  Mr.  Campbell  Swinton,  but  I  think  the 
argument  used  by  him  ought  to  have  the  negative  sign  put  before  it, 
because  the  conditions  in  the  case  of  incandescent  gas  are  exactly  the 
opposite  of  what  they  are  here.  In  the  case  of  the  incandescent  gas 
lamp,  if  you  increase  the  emissivity  of  the  mantle  you  lower  its 
temperature  and  eventually  its  candle-power.  But  the  mantle  gets 
more  energy  and  gives  more  out,  because  it  gains  more  from  the  gas, 
and  the  whole  question  is  different.  What  I  think  probably  happens 
in  the  case  of  the  Nernst  lamp  is,  that  when  the  glower  lamp  gets  a 
little  old  the  platinum  from  the  contacts  gets  into  the  body  and  you 
notice  a  slight  graying  of  the  filament,  and  this  means  an  increased 
emissivity  and  light-radiating  power  at  a  given  temperature.  And  if 
you  keep  the  watts  constants  it  radiates  energy  at  a  lower  temperature 
and  probably  gives  loss  light.  Mr.  Swinton's  experiments  in  bombard- 
ing thoria  are  not  in  the  least  conclusive,  either  as  regards  the  Nernst 
lamp  or  with  respect  to  incandescent  lamps  for  gas.  When  you  are 
bombarding  you  cannot  tell  whether  the  surfaces  are  at  the  same 
temperature,  though  they  may  look  so.  If  you  take  the  trouble  you  can 
find  on  purifying  zirconia  that  eventually  you  can  get  a  material  which 
you  can  make  into  mantles  for  gas  lamps  to  give  almost  no  light,  but 
they  will  give  plenty  as  Nernst  lamps,  and  they  will  give  plenty  of  light 
when  they  are  bombarded.  But  that  is  a  different  thing,  because  when 
you  are  bombarding  you  have  not  necessarily  got  them  at  the  same 
temperature. 


903.] 


THE  NERNST  LAMP  :    DISCUSSION. 


537 


Earl  Russell  {communicated) :  Not  being  able  to  get  into  the  room  EariRosseiL 
to  take  part  in  the  discussion,  I  am  compelled  to  send  some  observa- 
tions in  writing.  The  Nemst  lamp  is  a  very  fascinating  invention,  and 
the  account  by  Mr.  Stottner  is  very  interesting,  as  I  do  not  doubt  the 
exhibits  were  if  I  had  only  been  able  to  see  them.  The  lamp  is 
economical,  and  the  light  given  by  it  is  of  a  very  pleasing  quality. 
But  I  am  afraid  a  great  deal  has  yet  to  be  done  in  making  the  burner 
run  for  a  sufficient  time.  I  have  two  Pattern  A  1902  Nernst  lamps,  and 
my  experience  with  them  has  been  unfortunate.  The  lamps  are 
105-volt,  and  they  are  run  from  accumulators  only  in  which  the  usual 
pressure  is  loi  to  102  and  never  exceeds  104,  so  that  they  are  not  over- 
run. Nevertheless,  I  find  that  instead  of  a  life  of,  say,  300  hours,  as 
stated  in  the  catalogue,  the  average  life  has  been  something  like  20  hours. 
The  longest  that  any  burner  has  run  is  about  3  months  during  the 
lighter  part  of  the  year,  representing  perhaps  180  hours.  On  the  other 
hand  I  have  had  two  burners  going  the  next  day  after  being  put  in : 
two  which  refused  to  Hght  at  all,  and  three  or  four  which  had  gone  in 
periods  var)ring  fron  9  hours  to  40  hours.  It  is  only  fair  to  say  that 
so  far  the  Electrical  Company  have  been  most  generous  in  replacing 
these  early  failures  without  charge,  but  of  course  one  cannot  say  how 
long  that  will  go  on.  They  practically  always  break  at  the  same  place, 
that  is  the  spiral  part  near  the  bottom.  Another  objection  to  their 
commercial  use  at  present  is  the  limited  range  of  candle-power,  e.g.^ 
you  cannot  get  more  than  a  60-candle  lamp  on  a  loo-volt  circuit. 
Although  the  replacement  is  easy,  still  it  involves  time  and  annoyance 
(particularly  if  it  has  to  be  done  in  the  dark)  and  the  fetching  of  a  pair 
of  steps,  besides  the  cost  of  2s.  6d.  a  burner.  Until,  therefore,  a  longer 
average  life  can  be  given  to  the  burners,  I  fear  the  lamp  can  hardly  be 
regarded  as  a  success  for  use  in  private  houses. 

Mr.  A.  Wilson  {communicated)  :  I  am  disappointed  to  find  in  the  Mr.  Wiiwn. 
paper  no  statement  as  to  the  average  life  of  the  burners  and  resistances 
of  the  Nernst  lamps  as  at  present  placed  on  the  market,  and  should  be 
glad  if  the  author  would  give  some  information  on  that  point.  The 
Company  who  have  introduced  these  lamps  have  stated  in  one  of  their 
pamphlets  that  the  life  of  the  burner  averages  400  hours,  but  experience 
with  a  considerable  number  of  lamps  leads  me  to  believe  that  200  hours 
is  a  long  life,  and  even  that  can  only  be  attained  by  running  the  lamps 
coosiderably  below  the  total  volts  for  which  the  combined  burner  and 
resistance  are  marked.  For  example,  in  a  factory  in  which  over  100 
Umps  are  used,  with  220-volt  burners  and  20-volt  resistances  and  with 
never  more  than  about  240  volts  at  the  lamp  terminals,  the  engineer  in 
charge  stated  that  the  average  life  of  the  lamps  was  about  40  hours. 
By  using i  a  255-volt  combination,  i.e.,  235- volt  burner  and  20-volt 
resistance,  and  consequently  under-running  the  lamp  by  15  volts,  the 
life  has  been  raised  to  about  200  hours,  or  about  half  of  what  it  is 
supposed  to  be,  with,  of  course,  a  corresponding  reduction  in  the 
efficiency  of  the  lamp. 

The  lamps  undoubtedly  give  good  light  and  are  of  high  efficiency, 
but  the  unreliability  of  the  burners  and  the  amount  of  attention 
required  in  niaking  replacements  seems  more  than  to  balance  any 


538 


STOTTNER  :    THE   NERNST  LAMP. 


[Feb.  26th 


economy  which  they  are  supposed  to  effect.  I  am  quite  unable  to 
reconcile  the  statements  which  have  been  published  as  to  the  life  of 
the  lamps  with  my  own  experiences  and  those  of  many  others  under 
ordinary  working  conditions,  and  take  this  opportunity  of  asking  for  a 
statement  on  the  matter  from  one  who  is  apparently  intimately 
associated  with  the  manufacture  of  the  lamp. 

Mr.  J.  Stottner,  in  reply,  said  :  With  regard  to  the  remark  made 
by  Mr.  Drake  about  two  filaments  in  one  lamp,  the  construction  is 
shown  in  Fig.  F. 


I — vVW 


Fig.  F. 


We  put  two  filaments,  which  are  connected  in  parallel,  inside  the 
heater,  the  current  passing  through  one  automatic  cut-out  to  the  other 
pole.  One  or  other  of  the  two  filaments  will  be  heated  first — it  is 
immaterial  which — and  as  soon  as  one  is  incandescent  the  heat 
radiating  from  it  will  start  the  other  filament  and  make  it  also  a  con- 
ductor, so  that  there  are  two  filaments  and  one  conductor.  Another 
advantage  of  this  arrangement  is  that  if  one  filament  breaks,  or  for 
some  reason  goes  off,  the  other  is  always  intact  and  will  act  as  if 
nothing  had  happened. 

The  burners  with  horizontal  filaments  are  a  further  novelty,  they 
are  shown  in  Figs.  G,  H,  K,  and  L. 

The  filament  is  in  front  of  the  heater,  so  that  all  the  light  radiates 
directly  downwards ;  they  can  be  arranged  in  any  number.  In  these 
lighting  bodies  the  filaments  can  be  taken  out  and  easily  exchanged, 
the  complete  burners  being  fixed  in  the  body  of  the  lamp  as  in  the 
present  design.  The  filaments  are  exceedingly  simple  and  provided 
with  flexible  conductors,  which  carry  a  small  plug  on  each  end  for 
connecting  up.    One  hundred  filaments  can  be  got  into  a  match-box. 

Mr.  Hammond,  I  am  very  glad  to  say,  got  about  the  same  results  as 
the  Physikalische  Technische  Reichsanstalt,  which  worked  out  the 
average  life  of  a  lamp  at  about  450  hours,  while  Mr.  Hammond  got 
305  hours.     Had  he  had  such  clever  experts  to  handle  the  lamps  at 


1903.] 


THE   NERNST  LAMP  :    DISCUSSION. 


539 


Hackney  as  they  have  at  the  Physikalische  Technische  Reichsanstalt,  ^r-  ^^^ 
the  results  would  doubtless  have  been  still  better.    The  reason  why 
the  flexible  at  Hackney  and  many  other  places  has  failed  is  a  very 
simple  one. 


1 


} 


Fig.  G. 


o~^ 


Fig.  H. 


Fig.  K. 


The  heater-coil,  Fig.  M,  expands  somewhat  as  soon  as  it  is  up  to 
temperature,  and  if  the  flexible  wire  a,  which  conducts  the  current  to 
the  filament,  is  bent  and  touches  the  heater,  it  either  burns  through  at  6, 
should  there  be  a  bright  spot  in  the  heater  spiral,  or  it  burns  the  heater 
wire  through,  as  the  resistance  from  6  to  c  is  very  small.    There  would, 


///M\\       /''\\^ 

/  /  /  n  \  \    /  / 
i  \  ^ 
•  1  *      •  .  \  ^ 

Fig.  L. 


Fig.  M. 


however,  be  no  difficulty  in  taking  such  a  slight  precaution  as  to 
examine  the  filament  after  insertion.  If  the  lamp  does  not  light  up,  the 
automatic  cut-out  does  not  act  properly.  The  filaments  and  heaters 
must  be  examined  before  they  are  put  in,  and  if  the  heater  does  not 
cease  glowing  as  soon  as  the  filament  is  incandescent,  the  contact- 
spring  of  the  automatic  cut-out  sticks  and  the  inside  of  the  lamp  must 
be  examined. 


540 


STOTTNER  :    THE   NERNST  LAMP.  [Feb.  26th, 


Mr. 
StStlncr. 


The 
President. 


As  mentioned  by  Mr.  Swinburne  in  reply  to  Professor  Ayrton,  the 
efficiency-curve  of  the  lamps  which  Mr.  Drake  showed  is  very  high. 
We  have  not  found  such  very  high  efficiency  in  ours.  The  light 
certainly  does  go  down  after  a  lamp  has  been  in  use  for  a  considerable 
time,  and  the  filament  takes  longer  to  heat  up  than  it  does  when  it 
is  new.  The  efficiency  drops  considerably  because  of  the  blackening 
of  the  heater-coil  and  further  on  account  of  the  crystallisation  in  the 
filament,  as  is  shown  by  a  filament  on  the  table  before  me,  which  has 
burned  i,6oo  hours.  As  to  the  variation  of  voltage,  5  per  cent,  does 
not  make  any  material  difference  to  the  life  of  a  lamp,  but  it  is  prefer- 
able for  it  to  go  down  than  up.  There  was  one  station  mentioned, 
however,  where  the  variation  is  a  good  deal  higher  than  5  per  cent. 
There  may  be  a  20  per  cent,  variation.  If  the  voltage  rises  too  high, 
the  result  is  that  the  bolstering  resistance  burns  through.  It  acts 
as  a  kind  of  safety-fuse  to  the  lamp  if  everything  else  is  properly 
arranged. 

As  touching  the  question  whether  alternating-  or  direct-current 
lamps  are  the  better  ; — theoretically,  alternating-current  lamps  should 
be  better  but  practically  we  find  that  direct-current  lamps  give  greater 
satisfaction.  Whether  this  is  because  at  the  works  the  demand  for 
alternating-current  in  proportion  to  that  for  direct-current  lamps  is 
about  I  :  500,  and  less  experience  has  been  gained,  or  whether  there  is 
some  other  ground  for  this,  I  cannot  say.  The  breaking  of  filament  is 
generally  due  to  mechanical  causes.  Either  they  get  knocked  about,  or 
they  break  through  vibration  or  through  some  other  part  of  the  lamp 
not  acting,  as  already  mentioned.  The  electrolytic  effect  on  the  fila- 
ment will  in  every  case  be  exactly  the  same.  There  is  no  reason  why 
one  filament  should  burn  out  more  quickly  through  electrolysis  than 
another. 

One  speaker  mentioned  the  packing  and  transport,  which  is  a  very 
serious  question,  under  which  we  have  to  suffer  greatly.  As  a  test  of 
average  breakage  we  took  two  packages  and  tumbled  them  down  four 
Eights  of  stairs.  On  examination  we  found  in  one  case  two  burners 
broken  out  of  200  and  in  the  other  case  five  broken  out  of  400,  which  I 
do  not  think  is  a  very  great  percentage.  With  the  new  packing  it  will 
be  less  still.  The  old  packing  was  much  less  suitable  for  rough 
handling  in  transit.  I  once  caught  one  of  our  boys  tossing  three  of  the 
old-style  round  boxes  with  burners  like  a  juggler,  which  at  once  ex- 
plained to  me  why  some  of  the  filaments  break ;  and  other  people  may 
have  similarly  playful  boys  in  their  employ. 

The  President  :  I  will  now  ask  the  meeting  to  pass  a  very  cordial 
vote  of  thanks  to  Mr.  Stottner ;  and  I  have  his  authority  to  mention 
that  he  hopes  to  present  to  the  Institution  museum,  samples  showing 
the  early  history  of  this  lamp. 

The  vote  was  carried  by  acclamation. 

The  President  announced  that  the  scrutineers  reported  the 
following  candidates  to  have  been  duly  elected,  viz. : — 


1908.] 


ELECTIONS. 


641 


Member, 
WUson  Hartnell. 


Associate  Members, 


Frank  Bradford. 
Ashton  Bremner. 
Henry  Coulson-Crawford. 
James  Cuninghame. 


Albert  William  Davies. 
Raymond  G.  Mercer. 
Andrew  Home  Morton. 
Frank  J.  Robins. 


Associates. 


Augustus  George  Ashton. 


Malcom  Rayner  McClurc. 


Students. 

Arthur  McL.  Atkinson. 
Herbert  Frederick  H.  Blcase. 
John  Henry  Clarke. 
Ernest  Francis  Cutforth. 
James  Floyer  Dale. 
Walter  Hugh  St.  A.  Davies. 
Oswald  J.  Davis. 
Harold  W.  Fulcher. 
Henry  J.  Golding. 
George  Goodwin. 
Ernest  James  Harper. 
Laurence  E.  C.  Harrison. 
Herbert  H.  Harter. 
David  Cecil  Henderson. 
Frederick  Richard  Hobley. 
A.  T.  S.  Hore. 
James  G.  H organ. 
E.  Laubach. 
Horace  Hamilton  Leage. 

George  Stewaf  t 


William  E  Cato  Liebert. 
Wyndham  d'Arcy  Madden. 
Arthur  Cecil  Morrison. 
Ernest  William  Moss. 
Llewellyn  Digby  Odium. 
Hugh  Prideaux. 
Hubert  G.  Ross. 
Henry  Eustace  Sayer. 
Herbert  John  Seale. 
John  Franklin  Shipley. 
Chas.  Francis  Simpson. 
Benjamin  Spalding  Smith. 
Joseph  James  K.  Sparrow. 
Wm.  T.  Tallent-Bateman. 
David  Alan  Trickett. 
Eric  Charles  B.  Walton. 
Eric  Gordon  Waters. 
Thomas  Douglas  W.  Weston. 
Arthur  Penry  Williams. 
Wilson. 


642  HOLMES:  ADDRESS  AS  CHAIRMAN  [Newcastle, 


NEWCASTLE   LOCAL   SECTION. 

INAUGURAL  ADDRESS  OF  THE   CHAIRMAN. 
By  Mr.  J.  H.  Holmes,  Member. 

(ABSTRACT,) 
[Address  delivered  Ncn'cmber  17,  1902.) 

In  addressing  you  at  this,  the  third  inaugural  meeting  of  the 
Newcastle  Local  Section  of  the  Institution  of  Electrical  Engineers, 
I  wish,  in  the  first  place,  to  thank  you  for  the  honour  you  have  con- 
ferred upon  me  by  electing  me  to  the  position  of  your  Chairman  for 
the  ensuing  session. 

I  have  no  doubt  that  with  your  cordial  support  and  assistance  I 
shall  find  the  duties  appertaining  to  the  office  as  agreeable  as  they  are 
honourable,  and  that  our  united  efforts  will  enable  us  to  uphold  the 
status  of  the  Institution  and  make  the  session  a  success.  In  the 
remarks  which  I  have  the  privilege  of  addressing  to  you  by  way  of 
opening  our  proceedings,  I  propose  to  glance  at  the  influence  exercised 
by  the  great  activity  and  rapid  development  of  electrical  engineering 
upon  other  branches  of  the  engineering  profession. 

We  all  have  the  honour  of  belonging  to  the  noble  profession  of  the 
engineer  to  which  modern  civilisation  owes  so  much.  For,  whether 
it  is  within  the  sphere  of  the  domestic  circle  or  without,  in  the 
strenuous  life  that  daily  confronts  us,  there  is  scarcely  a  comfort  or  a 
convenience  that  exists  to  the  realisation  of  which  the  engineer  has  not 
largely  contributed.  Engineering  has  been  defined  as  the  art  of 
directing  the  great  sources  of  power  in  nature  to  the  use  and  con- 
venience of  man,  and  therefore  the  engineer  is  interested  in  every 
investigation  and  discovery  in  the  whole  realm  of  science — his  occupa- 
tion is  the  most  catholic  of  all.  No  sooner  does  an  abstract  theory 
become  a  demonstration  than  the  engineer  seizes  it  and  applies  it  to 
man's  uses. 

Some  discoveries  burst  upon  us  with  a  blaze  of  light  attracting 
universal  attention,  and  inventions  follow  with  lightning  speed,  whilst 
others  develop  so  slowly  as  almost  to  pass  unnoticed. 

The  branch  of  engineering  with  which  we  are  so  intimately 
concerned,  whilst  most  far-reaching  in  its  consequences,  is,  when 
measured  by  the  mere  lapse  of  time,  but  of  recent  growth,  yet, 
measured  by  its  phenomenal  progress,  is  quite  ancient,  and  already 
embraces  so  many  distinct  branches  that  it  has  become  practically 
impossible  for  one  man  to  keep  pace  with  the  developments  almost 
daily  occurring  in  its  many  sub-sections. 

Young,  however,  as  the  profession  of  electrical  engineering  is, 
I  think  wc  may  justly  claim  for  it,   that   it  has  exerted  a  greater 


1902.]  OF  NEWCASTLE  LOCAL  SECTION.  548 

influence  upon  engineering  as  a  whole  than  any  other  individual 
branch,  and  we  may  profitably  spend  our  time  by  glancing  at  a  few 
instances  of  the  kind. 

A  dynamo,  as  we  all  know,  is  the  agent  by  which  mechanical  power 
is  converted  into  electrical  energy.  The  prime  mover  is  usually  a 
steam  engine  which  has  a  reciprocating  motion,  which,  by  the  aid  of  a 
crank,  is  converted  into  a  turning  movement.  By  the  very  nature  of 
things  an  unequal  torque  is  the  consequence,  leading  to  a  pulsatory 
motion  of  the  dynamo.  There  is  no  more  exacting  duty  for  a  steam 
engine  than  that  of  driving  a  dynamo  for  any  purpose,  but  particularly 
for  lighting,  where  a  pulsation  or  rising  and  falling  in  the  intensity  is 
most  distressing.  Hence  in  the  early  days  to  drive  a  dynamo  by 
means  of  the  existing  engines  was  like  driving  a  square  peg  into  a  round 
hole,  and  the  steam  engineers  were  immediately  confronted  with  the 
problem  of  how  to  get  a  uniform  angular  velocity  which  was 
extraordinarily  important  in  running  alternators  in  parallel.  It  is 
interesting  to  recall  the  various  methods  employed  to  meet  the  case. 
How  eagerly  the  problem  was  struggled  with  more  or  less  satisfactorily 
in  many  different  ways. 

The  early  dynamos  were  run  at  high  speeds  obtained  by  belt- 
driving  through  gearings  or  countershafts,  which  was  soon  recognised 
as  wasteful  of  power,  and  the  difficulty  was  met  by  increasing  the 
engine  speeds,  which  drove  out  the  large  long-stroke  slow-moving 
heavy  engines  in  favour  of  small  short-stroke  quick-moving  light 
engines  driving  by  belting  direct  from  the  flywheel.  But  this  was  not 
enough,  because  dynamos  had  a  variable  load,  hence  the  makers  of 
small  engines  were  compelled  to  introduce  improved  governors  and 
heavy  flywheels.  These  took  the  form  of  high-speed  throttle 
governors  spring-controlled,  only  to  be  superseded  by  automatic 
expansion  governors,  which,  in  their  turn,  were  replaced  by  shaft 
governors  revolved  at  engine  speed. 

Heavy  flywheels  on  engines  used  specially  for  driving  dynamos  for 
traction  purposes,  where  the  alterations  in  load  are  both  frequent  and 
rapid,  did  very  good  service,  securing  a  relatively  constant  angular 
velocity  for  that  class  of  work. 

To  sum  up,  the  dynamo  with  its  high  speeds  forced  on  the  balancing 
and  governing  of  steam  engines  to  a  point  that  was  never  dreamed  of 
as  necessary  before. 

Another  problem  was  that  of  lubrication.  Continuity  of  run  over 
long  periods  called  attention  to  the  need  for  unfailing  lubrication,  the 
oil  cup  of  old  being  superseded  by  centrifugal  oilers,  and  a  few  hours' 
run  being  lengthened  out  into  fifteen  or  more,  and  finally  to  continuous 
running,  as  in  the  marine  engine.  This  led  to  the  employment  of 
pipes  and  wipers  fed  from  oil-cups,  and  later  from  a  central  oil-box 
with  sight  feeds.  Then  to  independent  oil-pipes  to  each  bearing 
surface,  conveying  oil  at  a  pressure  of  20  lbs.  to  the  square  inch,  main- 
tained by  a  force  pump.  And  perhaps  in  the  most  advanced  way  in 
enclosed  engines  such  as  the  Willans  or  Chandler,  where  the  moving 
p>arts  practically  splashed  about  in  a  bath  of  oil  and  water,  effectively 
lubricating  all  the  bearing  surfaces.     However,  all  experience  having 


644  HOLMES:  ADDRESS  AS  CHAIRMAN  [NewcasUe, 

shown  that  the  balancing  of  parts,  the  perfection  of  lubrication 
continuity  of  run,  small  occupation  of  valuable  space,  and  absence  of 
great  watchfulness  as  essentials  in  electrical  machinery  in  up-to-date 
power-houses,  it  is  brought  forcibly  home  to  every  one  that  in  Parsons' 
turbo-generator,  which  has  been  gradually  developing  of  recent  years, 
these  qualities  are  embodied,  combined  with  a  reasonable  steam  con- 
sumption, to  so  great  a  degree  as  to  bring  the  Hon.  C,  A.  Parsons' 
invention  into  the  foremost  rank  of  all  prime  movers,  and  I  am  sure  I 
voice  the  feeling  of  all  in  being  proud  to  note  that  our  esteemed 
member  has  been  awarded  the  Rumford  Medal  by  the  Royal  Society 
in  recognition  of  his  important  work.  Useful  as  this  steam  turbine  is 
in  electrical  work,  its  application  to  marine  propulsion  bids  fair  to  rank 
as  a  still  greater  achievement. 

Measurement  of  Power, — The  simplicity  and  exactitude  of  electrical 
measurements  has  exerted  a  very  great  influence  upon  questions 
relating  to  the  efi&ciency  of  steam  engines,  both  as  regards  steam 
consumption  and  the  internal  losses  in  the  engine  itself. 

Water  Cooling. — How  to  cool  water  for  condensing  purposes,  that 
great  aid  to  the  economical  application  of  steam  power,  is  one  of  the 
electrical  engineer's  difficulties  in  cities  where  cooling  ponds  and 
running  streams  are  absent.  This  has  been  met  by  the  introduction  of 
cooling  towers,  economical  at  their  load,  and  certainly  a  fairly  successful 
mode  of  meeting  what  is  a  difficulty  in  most  cases. 

Gas  Engines, — Strange  as  it  may  seem,  it  is  nevertheless  true  that 
it  was  many  years  before  the  electrical  engineers  could  convince  the 
gas-engine  makers  that  the  pulsation  in  lighting  from  gas-driven 
dynamos  was  not  inherent  to  the  dynamos. 

In  the  Otto  cycle  method  of  working,  where  the  compression  of  the 
mixed  gases  before  ignition  is  a  great  improvement,  in  the  single- 
cylinder  engine,  as  only  every  fourth  stroke  is  effective  (the  other  three 
absorbing  energy  stored  in  the  flywheel),  a  variable  angular  velocity 
results.  This  is  met  by  high  speeds  and  very  heavy  flywheels  placed 
on  the  engine,  which  is  the  right  place,  and  not  on  the  dynamo  spindle, 
which  is  the  wrong  place. 

As  the  heating  of  gas-engine  cylinders  is  proportional  to  the  work 
done,  over-heating  had  to  be  met  by  water  jacketing,  involving  in- 
creased tank  capacity  and  more  room  for  the  extra  cylinders,  a 
condition  unknown  in  intermittent  work  for  which  the  gas  engine  was 
in  the  main  designed  in  the  first  instance. 

Quite  recently,  large  power  producer-gas  engines,  such  as  the 
"  Diesel,"  consuming  crude  petroleum  finely  sprayed  into  the  combus- 
tion chamber,  have  been  introduced  highly  suitable  for  driving 
dynamos  with  economy. 

Transmission  of  Power, — In  the  transmission  of  mechanical  power 
I  claim  that  the  electrical  engineer  has  exercised  extraordinary 
influence. 

Belting, — ^The  increase  of  transmitted  power  through  using  higher 
speeds  in  running  shafting  and  belting  was  but  dimly  recognised  until 
forcibly  brought  under  notice  by  dynamo  working. 

Inequalities  in  laced  belting  joints  caused  jerks  in  running  over 


1902.]  OK  NEWCASTLE   LOCAL  SECTION  646 

d3mamo  pulleys,  and  'led  to  endless  §ewn  joints  for  smoothness  in 
running  and  dynamo  slide  rails  for  taking  up  the  slack  caused  by 
stretching. 

Then  to  obtain  greater  equality  and  avoid  slip  the  leather  link  belt 
was  devised,  each  link  becoming  a  joint.  The  extra  weight  of  this 
form  of  belt  was  of  advantage  when  used  with  the  top  side  slack,  as  it 
should  be,  as  its  sag  embracing  a  larger  arc  of  contact  on  the  pullies 
reduced  slip,  even  when  the  shafts  were  comparatively  close  together. 
But  a  laminated  belting  composed  of  long  strips  of  leather  placed  on 
edge  side  by  side  until  the  required  width  is  obtained,  then  closely 
sewn  through,  best  fulfils  the  requirements  for  the  transmission 
of  power. 

Small  Steam  Pipes. — The  great  economy  in  the  electric  transmission 
of  power  by  means  of  wire  conductors  has  opened  the  eyes  of  the 
owners  of  works  to  their  losses  in  that  most  wasteful  method  of  power 
transmission  by  distributing  steam  from  a  central  point  by  means  of 
steam  pipes,  either  underground  or  overhead,  to  small  engines  at  a 
distance.  Enterprising  men,  especially  shipbuilders,  have  realised 
large  economies,  first  by  diminishing  labour  by  concentrating  their 
generating  plant  in  one  shop,  and,  secondly,  by  replacing  their 
notoriously  inefficient  scattered  small  steam  engines  by  electric  motors 
deriving  their  energy  from  compound  or  ttiple  condensing  engines. 
The  electric  motor  only  draws  energy  as  the  work  needs  it,  the  waste 
in  distribution  by  electric  conductors  is  trifling,  the  daily  upkeep  is 
small,  and  the  arrangements  are  simple  in  control.  These  advantages 
presage  the  early  supersessions  of  steam-power  distribution,  and  also  of 
hydraulic-power  distribution.  Lifts  or  elevators  are  now  mostly 
electrically  worked,  and  cranes  and  capstans  for  docks  and  warehouses 
are  rapidly  following  suit 

In  overhead  travelling  cranes  the  usefulness  of  three  motors  versus 
one  motor  is  moving  in  favour  of  three  motors,  because  of  the  peculiar 
feature  of  electric  driving  previously  mentioned — the  absence  of  loss 
of  energy  excepting  during  actual  running  of  the  motor  which  exactly 
fits  intermittent  work. 

The  slow  speed  of  the  chain  drum  has  called  for  improvements  in 
gearing,  leading  to  the  use  of  raw-hide  gearing,  double  or  triple  thread- 
worm gearing  running  in  an  oil  bath,  of  friction  gear,  and  in  some  cases 
the  epicycle  train. 

The  propulsion  of  vehicles  is  of  immense  importance,  and  the 
electric  influence  is  daily  more  marked.  Indeed,  it  is  evident  that  we 
are  on  the  threshold  of  huge  developments  in  this  direction. 

Even  the  large  railway  companies  have  been  stirred,  and  it  looks  as 
if  Newcastle,  the  birthplace  of  the  locomotive,  will  also  be  the  pioneer 
in  the  use  of  electric  haulage.  If  not,  it  is  safe  to  predict  that  the 
electric  tramways  service,  which  is  now  developing  so  marvellously, 
will  still  further  diminish  their  receipts. 

Electric  tramways  must  work  a  complete  revolution  in  social  life, 
inasmuch  as  their  cheap  rapid  and  pleasant  transit  brings  town  and 
country  into  closer  touch,  spreading  the  population  over  a  wider  area, 
discrediting  jerry-built  flats  in  favour  of  garden  cottages. 


546  HOLMES:  ADDRESS  AS   CHAIRMAN  [Newcastle, 

For  all  automobile  work  electricity  is  by  far  the  cleanest  and 
most  agreeable  agent,  and  much  development  may  be  looked  for  in 
this  direction. 

Socially,  the  influence  of  the  electric  light  has  been  most  marked  ; 
it  has  lent  brilliancy  to  internal  lighting  by  the  use  of  the  arc,  and  for 
decorative  purposes  the  glow-lamp  is  supreme,  whether  it  be  for 
advertisement  or  for  social  gatherings.  It  has  stimulated  the  use  of 
light ;  that  which  used  to  be  considered  sufficient  is  now  considered 
inadequate,  what  would  formerly  poison  the  atmosphere  and  dirty  ali 
decoration  now  simply  makes  home  cheerful,  and  vitiation  of  the  air 
is  overcome  whether  in  the  theatre  or  the  home. 

The  reaction  upon  the  gas  industry  has  been  immense  ;  the  gas  man's 
monopoly  has  gone,  and  with  it  his  lethargy,  leading  to  the  regenerative 
gas-burners  of  Siemens  and  Wenham,  and  the  Welsbach  light ;  and, 
latterly,  the  Kitson  modification  of  the  Welsbach,  with  its  low  cost  and 
rivalry  of  the  electric  light  ?  Similarly  in  fittings,  the  artistic  designs  in 
graceful  lines  to  please  architects  have  stimulated  similar  improvements 
in  gas-fittings.  And  as  to  ocean  steamers,  what  would  they  be  without 
the  electric  light  ?  and  shortly  what  will  they  be  without  electric 
winches,  windlasses,  fans,  which  are  fast  superseding  small  engines 
and  leaky  steam-pipes  ? 

Then,  again,  what  an  influence  electric  search  and  other  lights  have 
had  on  the  mercantile  marine,  doubling  the  capacity  of  the  Suez 
Canal  without  cost,  where  90  per  cent,  of  the  vessels  that  pass  through 
save  fourteen  hours  per  trip  by  its  agency. 

The  coal  miner  now  signals,  blasts,  and  lights  electrically  ;  also 
pumps,  hauls,  drills  and  cuts  his  coal  electrically. 

The  gold  miner  converts  water  power  into  electric  power,  and  by 
its  agency  crushes  ores  and  uses  it  for  all  mechanical  purposes. 

Edison  separates  iron  ores  formerly  useless  for  the  smelter,  and 
electricity  plays  a  prominent  part  in  reducing  and  refining,  whilst  the 
electric  furnace  also  produces  aluminium,  sodium,  carborundum,  and 
calcium  carbide  now,  and  will,  probably,  other  substances  shortly. 

Of  course  of  the  oldest  of  the  electrical  industries,  telegraphy,  and  its 
development  telephony,  much  can  be  said  ;  what  was  a  luxury  is  now 
a  necessity  almost  as  much  as  the  sun  itself,  for  by  its  commercial 
agency  the  business  of  equalising  the  products  of  the  world  for  feeding 
its  inhabitants  is  consummated. 

As  for  wireless  telegraphy,  with  which  Marconi's  name  is  linked  for 
ever,  it  should  be  as  useful  to  fleets  at  sea  as  the  ordinary  telegraph  is 
to  railways  on  land,  and  what  more  may  be  in  store  only  time  will 
reveal. 

Again  in  the  case  of  the  body,  for  nervous  troubles,  for  baths,  for 
cauterising,  for  ameliorating  skin  diseases  and  looking  into  our 
interiors  with  Rontgen  rays,  how  can  we  do  without  it  ? 

I  trust  this  rapid  glance  at  some  of  the  instances  of  the  influence  of 
electrical  on  other  branches  of  engineering  has  served  to  remind  us 
that  we  belong  to  a  profession  which,  though  young,  has  played  an 
important  part  in  the  march  of  progress  recently,  and  promises  a  more 
rapid  advance  than  ever   now.      Electricity  now    permeates    every 


1902.]  OF  NEWCASTLE   LOCAL  SECTION.  547 

branch  of  business  ;  it  is  no  longer  an  abstruse  science,  and  every  one 
who  takes  an  intelligent  interest  in  what  goes  on  around  him  must 
acquire  some  knowledge  of  its  behaviour  ahcl  uses. 

By  creating  new  needs  electricity  has  stimulated  the  other  branches 
of  the  profession  in  a  very  marked  manner,  quite  beyond  the  stimulus 
of  competition  in  their  own  lines. 

It  would  be  too  big  a  subject  to  enter  upon  the  question  as  to  how 
far  our  present  standard  of  civilisation  would  be  possible  if  electricity 
were  absent  from  our  calculations,  and  I  must  leave  this  for  each  of 
us  to  think  out  for  himself. 

If  I  have  succeeded  in  impressing  upon  any  one  of  my  hearers 
a  higher  opinion  of  the  usefulness  and  importance  of  the  work  upon 
which  he  is  engaged,  and  of  the  nobility  of  his  profession,  I  shall  be 
amply  repaid  for  what,  after  all,  arc,  I  fear,  but  feeble  efforts  to  do 
justice  to  a  theme  which  is  worthy  of  a  much  abler  pen  than  mine. 


648  LEA:    ADDRESS  AS  CHAIRMAN  [Birmingham, 

BIRMINGHAM  LOCAL   SECTION. 


INAUGURAL  ADDRESS  OF  THE   CHAIRMAN, 
By  Mr.   Henry   Lea,   Member. 

(ABSTRACT,) 
(Address  delivered  December  lothy   igo2,) 

From  time  to  time,  particularly  since  the  advent  of  electricity  as  a 
producer  of  light  and  a  distributor  of  motive  power,  we  English 
engineers  have  been  charged  with  being  laggards.  I  am  not  one  of 
those  who  believe  that  we  are  in  a  bad  case,  and  I  propose  to  try  this 
evening  to  ascertain  whether  the  state  of  one  industry  at  all  events, 
namely  the  electrical  industry,  is  calculated  to  afford  encouragement 
to  ourselves  and  the  country  generally,  or  whether  the  gloomy  views  so 
often  expressed  are  in  any  sense  justified.  My  aim  this  evening  will  be 
to  obtain  a  general  idea  whether  the  Electrical  Industry  is  growing,  or 
standing  still,  or  going  backwards.  The  period  selected  for  scrutiny 
comprises  the  years  1898 — 1901,  four  years  being  quite  enough,  in  my 
judgment,  to  show  which  way  the  stream  is  flowing. 

The  first  point  that  I  shall  bring  before  you  relates  to  the  growth  of 
the  manufacture  of  steam  engines  for  driving  dynamos.  Nineteen 
large  firms  were  good  enough  to  respond  freely  to  my  inquiries.  The 
results  which  I  shall  place  before  you  are  the  collective  totals  of  the 
returns  of  all  the  firms  who  have  been  good  enough  to  give  them  in 
each  case,  and  whilst  they  must  not  be  taken  as  being  in  any  sense  the 
totals  of  this  country's  production,  they  may,  I  think,  be  fairly  regarded 
as  representative  of  the  industry  generally. 

Steam  Engines. 

Confining  myself  then  at  present  to  steam  engines  made  by  nineteen 
firms  only,  I  find  the  following  results  : — 

1.  Numbers  of  Steam  Engines  turned  out  for  the  sole  purpose  of  driving 
Dynamos  : — 

1898.— 967. 

1899. — 1,649,  an  increase  of  71  per  cent,  over  1898. 
1900. — 1,655,  an  increase  of,  say,  i  per  cent,  over  1899. 
1901. — 1,836,  an  increase  of  11  per  cent,  over  1900. 
1901  shows  an  increase  of  90  per  cent,  over  1898. 

2.  B.H,P,  of  the  same  Engines  in  nearest  round  numbers  : — 

1898.-86,000. 

1899. — 168,000,  an  increase  of  96  per  cent,  over  1898. 
1900. — 210,000,  an  increase  of  25  per  cent,  over  1899. 
1901. — 295,000,  an  increase  of  41  per  cent,  over  1900. 
1901  shows  an  increase  of  243  per  cent,  over  1898. 


1902.]  OF  BIRMINGHAM   LOCAL  SECTION.  649 

The  extremely  rapid  growth  in  horse-power  as  compared  with  the 
much  slower  growth  in  numbers  of  engines  indicates  that  the  sizes  of 
the  engines  are  increasing.    Thus, 

3.     A  verage  Horse-Power  per  Engine  : — 

1898.— 89  H.P.  each. 

1899. — 102   „       „      an  increase  of  15  per  cent,  over  1898. 

1900. — 127  „       „      an  increase  of  26  per  cent,  over  1899. 

1901. — 161   „       „      an  increase  of  24  per  cent,  over  1900. 

1901  shows  an  increase  of  81  per  cent,  over  1898. 

I  think  you  will  agree  that,  at  all  events  as  regards  steam  engines  for 
producing  electricity,  there  has  been  nothing  during  the  last  four  years 
to  dishearten  the  people  of  this  country 

Continuous-current  Machinery. 

Now  let  us  turn  to  the  output  of  dynamos  and  motors,  taking  first 
continuous-current  machines.  In  this  connection  the  number  of  finps 
furnishing  returns  is  17  only. 

1.  Numbers  of  Coniinuous-currcni  Machines,  including  both  Dynamos 
and  Motors  : — 

1898.-2,540. 

1899. — 4,736,  an  increase  of  86  per  cent,  over  1898. 
1900. — 5,095,  an  increase  of  7  per  cent,  over  1899. 
1901. — 6,799,  ^^  increase  of  33  per  cent,  .over  1900. 
1901  shows  an  increase  of  168  per  cent,  over  1898. 

2.  Power  of  Continuous-current  Dynamos  and  Motors  in  Kilowatts 
(nearest  round  numbers) : — 

1898.—  39,300  K.W. 

1899. —  65,200  K.W.,  an  increase  of  63  per  cent,  over  1898. 

1900. —  83,600  K.W.,  an  increase  of  28  per  cent,  over  1899. 

1 901. — 107,400  K.W.,  an  increase  of  40  per  cent,  over  1900. 

1901  shows  an  increase  of  174  per  cent,  over  1898. 

A  fact  that  has  become  evident  during  the  last  four  years  has  been 
the  growth  in  the  use  of  multipolar  machines  for  continuous  currents. 
The  matter  is  not  very  well  understood,  and  manufacturers  have  been 
largely  in  the  hands  of  consulting  engineers.  A  multipolar  machine 
can  be  constructed  at  low  cost  to  give  very  high  efficiency  as  regards 
CR  losses,  but  it  is  a  much  more  difficult  matter  to  get  over  iron  losses. 
The  last  four  years  have  seen  a  great  increase  of  knowledge  on  this 
subject.  The  correct  construction  and  subdivision  of  the  magnet 
cores,  the  correct  proportioning  and  the  number  and  size  of  slots  in  the 
slotted  armature  cores,  have  during  the  past  four  years  received  increas- 
ing attention,  so  that  if  we  now  compare  the  most  economical  multi- 
polar machine  with  the  most  economical  bipolar  smoothed  core  arma- 
ture of  ten  years  ago,  we  find  the  former  has  at  length  equalled  the 


660  LEA:    ADDRESS  AS   CHAIRMAN  [Birmingham, 

economical  efficiency  of  the  latter  ;  whereas  for  a  long  time  following 
the  first  introduction  of  multipolar  machines,  although  they  were  always 
a  better  mechanical  job  they  were,  on  account  of  their  heavier  iron 
losses,  behind  the  older  machines  in  efficiency.  Consumers  as  a  rule 
did  not  appear  to  understand  this,  and  demanded  the  same  high  effi- 
ciency from  the  modern  multipolar  that  they  were  in  the  habit  of 
obtaining  from  the  old  smooth-cored  bipolar,  but,  for  the  foregoing 
reasons,  manufacturers  failed  for  a  long  time  to  turn  out  multipole 
dynamos  or  motors  within  the  specified  limits  of  efficiency. 

Ten  years  ago  the  iron  and  core  losses  of  the  bipolar  machines 
made  by  several  leading  firms  were  under  i  per  cent,  but  the  C'R 
losses  were  only  kept  down  to  3  per  cent,  by  the  profuse  and  costly 
use  of  copper  in  the  armatures  and  fields.  In  these  days  the  same 
total  efficiency  is  obtained,  but  the  distribution  of  losses  is  reversed  ; 
the  C'R  losses  can  be  kept  down  to  i  per  cent.,  while  the  core  losses 
are  with  difficulty  reduced  to  3  per  cent. 

Alternating-current  Machinery. 

The  makers  of  this  class  of  machinery  are  comparatively  few  in 
number,  and  as  regards  three-phase  work  have  not  long  been  engaged 
in  the  production  of  such  machines.  The  most  that  the  returns  show 
is  that  this  branch  of  British  industry  is  receiving  some  attention, 
though  real  activity  of  growth  has  yet  to  come.  Grouping  together 
single-phase,  two-phase,  and  three-phase  machines,  the  following  are 
the  results  of  the  returns  (from  five  firms)  of  generators  and  motors 
combiried  ; — 

1898. — 35  machines,  output  9,322  K.W. 

1899.— 37        „  „      8,974    „ 

1900.— 39        „  „      8,209    » 

1901.— 77        „  „      8,165    „ 

The  increase  in  the  output  of  polyphase  machinery  abroad  is  due 
in  the  main  to  the  fact  that  local  conditions  gave  rise  to  a  demand  for 
it,  whereas  no  demand  for  this  class  of  machinery  existed  at  home. 
Moreover,  the  position  of  the  patents  is  very  ill-defined,  and  few  firms 
here  have  thought  it  worth  while  to  lay  themselves  open  to  an  infringe- 
ment action  simply  to  be  able  to  fill  a  limited  number  of  orders  for 
power  distribution  and  mining  work.  No  doubt  this  position  will 
soon  alter  itself,  though  as  regards  the  use  of  polyphase  machinery  in 
ordinary  factory  work  the  want  of  flexibility  of  speed  control  militates 
against  its  application  in  this  direction,  where  minute  speed  regulation 
appears  to  be  of  increasing  importance. 

Standardisation. 

Although  there  certainly  has  been  a  very  substantial  increase  in  the 
output  of  electrical  plant  during  the  four  years  which  I  have  selected 
for  comparison,  yet  it  is  probable  that  the  increase  would  have  been 
still  greater  if,  a  few  years  ago,  the  engineering  interests  concerned 
could  have  arranged  for  a  certain  amount  of  standardisation.    Consider 


1902.]  OK   BIRMINGHAM   LOCAL   SECTION.  551 

two  firms  of  equal  size  and  equal  manufacturing  capacity,  one  of  which, 
"  A,"  manufactures  50  patterns,  and  the  other,  "  B,"  manufactures 
100  patterns,  both  following  the  modern  principle  of  manufacturing 
compK>nents  and  afterwards  making  them  up  as  the  orders  come 
in.  With  an  equal  stock  of  tools  for  turning  out  these  components, 
and  with  equal  money  value  of  components  kept  in  stock,  the  firm  *' A  " 
that  works  on  only  50  patterns  will  be  able  to  execute  an  order  for  any 
one  of  these  patterns  in  half  the  time  that  the  firm  "  B  "  will  require 
that  has  100  patterns.  Then,  as  the  time  for  executing  the  order  is 
shortened,  so  may,  for  equal  dividends  paid,  the  price  per  article  be 
reduced.  The  firm  "A"  therefore  manufacturing  in  less  time  than 
*'  B,"  turns  over  its  capital  in  pro  rata  less  time  than  "  B,"  and  con- 
sequently may  be  satisfied  with  a  less  percentage  of  profit,  and  yet  pay 
an  equal  dividend.  Thus  quick  delivery  and  low  prices  go  together 
and  help  one  another  to  enable  the  firm  "A"  to  keep  its  order  sheets  full. 

I  imagine  that  no  manufacturing  firm  exists  that  would  not,  if  it 
could,  standardise  everything  it  makes,  and  work  to  jigs  and  templates 
throughout,  but  in  a  new  industry  experiencing  a  rapid  development 
it  is  not  possible  to  standardise  at  an  early  stage.  The  process  of  the 
survival  of  the  fittest  is  going  on  in  its  usual  relentless  fashion,  and  a 
too  early  endeavour  to  standardise  would  only  mean  a  heavy  loss  in  the 
abandonment  of  superseded  special  tools,  or  in  the  remodelling  of  them 
to  suit  the  inevitable  alteration  in  pattern.  Between  these  two  sets  of 
imperious  conditions,  on  the  one  hand  the  urgent  necessity  for 
standardising,  and  on  the  other  hand  the  danger  of  doing  so  too  soon, 
stands  the  manufacturer,  and  happy  is  he  whose  customers  realise  the 
desirability  of  establishing  standards  at  the  earliest  practicable  point  in 
the  history  of  the  development,  and  so  lend  a  hand  in  facilitating  the 
manufacture  of  interchangeable  machines. 

The  Institution  of  Civil  Engineers,  with  the  Institution  of  Mechanical 
Engineers,  the  Institution  of  Naval  Architects,  the  Iron  and  Steel 
Institute,  and  our  own  Institution,  have  now  a  joint  Standardising  Com- 
mittee in  full  swing,  and  there  is  hope  that  something  may  be  done  in 
the  matter,  and  that  consulting  engineers  and  manufacturers  may  find 
themselves  able  to  co-operate  towards  so  desirable  an  end. 

Power  Schemes. 

This  subject  is  wide  enough  for  a  long  special  paper  to  itself.  I 
cannot  do  more  than  briefly  refer  to  it.  The  scope  for  constructive 
business  is  enormous.  The  scope  for  skill  to  make  all  the  proposed 
schemes  pay  well  is  equally  great.  I  think  it  may  be  taken  that  it  will, 
generally  speaking,  be  no  part  of  the  Companies*  programmes  to  com- 
pete with  the  electric  light  undertakings  in  their  districts,  but,  on  the 
contrary,  to  assist  the  local  authorities  to  obtain  Provisional  Orders, 
and  to  supply  them  with  power  in  bulk,  which  they  may  retail  to  the 
inhabitants  of  their  areas. 

Traction  Work. 

Under  this  heading  I  include  tramways  and  light  railways,  but  not 
railways  other  than  light  railways.    The  progress  in  this  branch  of  the 
Vol.  32.  87 


662  LEA:    ADDRESS  AS   CHAIRMAN  [Birmingham, 

industry  has  been  marked,  but  not  nearly  so  rapid  as  in  the  other 
branches  previously  referred  to.  The  great  growth  has  yet  to  come, 
and  there  are  indications  that  it  will  be  of  vast  proportions. 

The  number  of  firms  who  in  this  country  make  tramway  motors  is 
very  limited,  but  the  industry  is  rapidly  growing.  From  the  returns 
which  I  have  received,  the  output  for  the  year  1901-2  was  nearly  40  per 
cent,  in  excess  of  the  output  for  the  year  1900-1.  Of  the  total  number 
of  cars  now  running  in  England,  upwards  of  80  per  cent,  of  them  have 
motors  manufactured  in  England,  and  the  importation  of  such  machinery 
is  decreasing  rapidly. 

I  will  present  to  you  the  growth  from  two  points  of  view,  namely, 
(i)  the  mileage  and  number  of  cars  ;  and  (2)  the  amount  of  capital 
invested. 

I.  Route  Mileage  and  Number  of  Cars. 

ROUTE  MILEAGE. 
1898.-365. 

1899. — 478  =  31  per  cent,  increase  over  1898. 
1900.-576  =  20    „  „    1899. 

1901.-777  =  35    „  „    1900. 

1901  shows  an  increase  of  112  per  cent,  on  1898, 

NUMBER  OF  CARS. 

1898.-2,117. 

1899. — 2,654  =  22  per  cent,  increase  over  1898. 
1900.-3,033  =  14        „  „        1899. 

1901.-3,821  =  26        „  „        1900. 

1 90 1  shows  an  increase  of  73  per  cent,  on  1898. 

2.  Capital  Invested  (nearest  round  numbers). 


1898 

Companies 

9,800,000 

1899 

Companies 

11,800,000 

Municipalities  ... 

1,170,000 

12,970,000 

=  33  per  cent,  increase  over  1898 

1900 

Companies 

14,560,000 

Municipalities  ... 

2,750,000 

1*7  '5  in  rtrtt\ 

*7>3**^»^^^^^ 

=  33  per  cent,  increase  over  1899 

I90I 

Companies 

19,750,000 

Municipalities  ... 

10,520,000 
30,270,000 

=  75  per  cent,  increase  over  1900. 
1901  shows  an  advance  of  210  per  cent,  increase  over  1898. 

It  may  be  of  interest  here  to  remind  you  of  two  examples  of  tram- 
way work  carried  out  on  novel  lines.  At  Wolverhampton  we  have  the 
Lorain  surface -contact  system  at  work,  so  far  successfully,  though  a 
crucial  test  would  be  a  severe  winter  with  plenty  of  snow  and  salt- 
Then  in  London  we  have  an  extensive  conduit  system  about  to  get  to 
work. 


1902.]  OF  BIRMINGHAM   LOCAL  SECTION.  663 

Electrificatiox  of  Main  Lines  of  Railways. 

On  the  North  Eastern  Railway  a  portion  of  the  system  is  about  to  be 
electrified  upon  a  good  working  scale,  and  much  practical  information 
will  no  doubt  be  derived  from  it  later  on.  It  may  be  regarded  as  the 
first  attempt  in  this  country  to  displace  existing  locomotives.  The 
converted  hues  will  be  those  running  from  Newcastle-on-Tyne  to 
Gosforth,  with  some  smaller  branches.  The  main  object  of  the  con- 
version from  steam  to  electricity  is  to  compete  with  the  electric  trams, 
so  that  the  scheme  will  be  laid  out  as  much  as  possible  to  look 
primarily  after  the  passenger  traffic. 

The  employment  of  electricity  for  the  special  purposes  of  under- 
ground railways,  or  for  a  new  overhead  line  as  in  Liverpool,  can  hardly 
be  looked  upon  in  the  same  light  as  the  N.  E.  R.  experiment,  which  is 
undoubtedly  in  the  direction  of  displacing  steam  locomotives  from  the 
ordinary  main  lines  of  railway  in  this  country.  It  is,  however,  a  far 
cry  from  motor  coaches  of  i6o  H.P.  each  to  trains  requiring  engines  to 
work  them  capable  of  developing  up  to  i,ooo  H.P.,  which  power  can  be 
exerted  by  some  of  our  main-line  engines.  The  steam  locomotive  may 
be  doomed,  but  I  cannot  help  thinking  that  it  will  die  hard,  and  I  for 
one  shall  be  very  sorry  when  they  are  no  longer  to  be  seen  doing  the 
excellent  work  which  they  undoubtedly  can  do.  When,  however,  this 
country  has  been  cleared  of  them,  I  shall  probably  not  be  here  to  see 
the  result. 

A  great  deal  has  been  said  from  time  to  time  to  the  effect  that  by 
means  of  electricity  alone  and  a  straight  mono-rail  track,  speeds  of  loo 
miles  an  hour  become  possible,  and  that  one  reason  for  this  is  that  the 
employment  of  reciprocating  parts,  as  in  an  ordinary  locomotive, 
prohibits  their  use  for  those  speeds.  In  my  judgment  there  is 
absolutely  no  foundation  for  this  statement.  The  only  reason  why  our 
locomotive  engineers  have  not  hitherto  enabled  us  to  travel  at,  say,  loo 
miles  an  hour,  is  that  they  have  never  been  asked  to  do  so,  and  if  asked, 
have  not  had  suitable  roads  with  suitable  curves  and  suitable  gradients 
for  doing  so.  If  it  were  decided  to  run  at  loo  miles  an  hour,  first  of  all 
it  would  be  necessary  to  lay  a  straight,  or  a  very  nearly  straight  track 
built  in  the  very  best  modern  style.  They  would  then  probably  elect 
to  draw  trains  of  the  same  length  as  those  proposed  to  be  drawn  on  the 
electrical  system,  namely,  one  or  two  long  corridor  coaches.  At 
323  r.p.m.  a  modern  locomotive  having  driving-wheels  6  ft.  6  in. 
diameter  travels  at  the  rate  of  75  miles  per  hour,  and  this  speed 
is  an  everyday  performance  on  our  main  lines.  The  presence  of 
reciprocating  parts  does  not  prohibit  such  speeds,  nor  do  the  engines 
appear  to  sufifer  therefrom.  I  have  it  from  one  of  our  most  eminent 
locomotive  superintendents  that  the  maximum  limit  might  be  fixed  at 
350  r.p.m.  Taking,  however,  the  above-named  lesser  and  everyday 
number  of  323  r.p.m.,  the  diameter  of  the  driving-wheels  for  100 
miles  an  hour  would  have  to  be  8  ft.  8  in.,  or  11  inches  only  larger  in 
diameter  than  the  7  ft.  9  in.  wheels,  numbers  of  which  are  already  to 
be  found  on  our  main  lines,  and  doing  excellent  work/  It  would  be 
absurd  to  pretend  that  a  locomotive  engine  with  8  ft.  8  in.  driving- 


664  LEA  :    ADDRESS  AS   CHAIRMAN  [Birmingham, 

wheels  could  be  built  to  take  one  of  our  long  trains  of,  say,  14  coaches 
at  anything  like  100  miles  an  hour ;  but  if  the  train  be  reduced  to  the 
length  proposed  for  electrical  propulsion,  then  a  steam  locomotive 
could  be  built  of  sufficient  power  to  deal  with  it,  and  if  the  reciproca- 
tions of  the  engine  were  kept  down  to  the  present  maximum  number 
per  minute,  there  would  be  no  more  difficulty  in  relation  to  the  recipro- 
cation of  the  parts  than  there  is  now.  The  conclusion  is  that  it  is  by 
no  means  necessary  to  fly  to  electricity  for  speeds  of  100  miles  per 
hour.  The  steam  locomotive  will  easily  give  those  speeds  if  they  are 
really  wanted  on  tracks  specially  laid  down  for  the  purpose.  The 
smoothness  and  steadiness  with  which  one  travels  at  75  miles  an  hour, 
or  even  at  the  86  miles  an  hour  which  have  been  attained  on  one  of 
our  main  lines,  preclude  entirely  any  apprehension  that  at  a  speed  of 
16  per  cent,  in  excess  of  86  miles  an  hour  the  smoothness  and 
steadiness  would  be  in  any  degree  inferior  upon  an  ordinary  first-class 
double-rail  track  laid  sufficiently  straight  for  the  purpose. 

Railway  Station  General  Purposes. 

On  the  London  &  North  Western  Railway  at  Crewe  extensive 
alterations,  involving  amongst  other  things  the  enlargement  of  the 
station  and  junctions,  the  addition  of  some  50  miles  of  sidings,  and  the 
erection  of  a  large  transhipment  goods  warehouse,  called  for  some  well 
considered  scheme  for  lighting  and  working  them.  For  power 
purposes,  instead  of  enlarging  or  reconstructing  the  hydraulic  plant, 
the  latter  has  been  abandoned,  and  electricity  alone  is  used  for  all 
purposes.      The  power-house  has  a  capacity  of  about  1,000  H.P. 

The  growing  utilisation  of  electricity  for  general  railway  purposes 
cannot  be  better  shown  than  by  quoting  the  following  instances  on  the 
N.E.  system  :  The  operation  of  travelling  jib  cranes  and  of  capstans  at 
Middlesbrough  and  West  Hartlepool,  the  equipment  of  the  York 
carriage  works  with  electric  overhead  travelling  cranes  and  motor- 
driven  machinery,  electric  overhead  conveyors  for  goods  at  York 
goods  warehouse  and  at  Newcastle,  electric  overhead  travelling  cranes 
at  the  Shildon  wagon  shops,  together  with  motors  for  driving 
punching,  shearing,  etc.,  machines ;  contemplated  experiments  with 
the  electric  lighting,  of  signals  at  Middlesbrough  and  Leeds  ;  at  York 
the  ticket-printing  machines  are  electrically  driven,  and  at  Newcastle 
the  ticket-destroying  machine;  the  new  locomotive  shops  at 
Darlington  are  also  being  equipped  with  large  electric  overhead 
travellers  for  lifting  locomotives,  etc.,  etc. 

Railways  Points  and  Signals. 

I  have  included  this  subject  because  points  and  signals  require  a 
considerable  amount  of  power  to  work  them  with  certainty  under  all 
conditions,  involving  the  use  of  electric  motors  for  the  purpose.  The 
examples  are  but  few  in  number,  and  indeed  I  am  unable  to  place 
before  you  any  particulars  other  than  those  which  Mr.  F.  W.  Webb,  of 
the  L.  &  N.  W.  Railway,  has  been  good  enough  to  send  me.  Ten  signal 
cabins  at  Crewe  are   now  worked   or  arc  about  to   be  worked  by 


1902,]  OF  BIRMINGHAM   LOCAL  SECTION.  566 

electricity.  In  all  they  will  contain  i,ooo  levers.  One  of  them  will 
contain  350  levers,  the  largest  signal  cabin  in  fhe  world.  The  whole 
are  interlocked  much  in  the  same  way  as  on  the  old  plan.  The  use  of 
them  does  not  involve  any  fresh  training  of  the  signalmen.  The 
levers  are,  in  fact,  switch  levers  only,  controlling  motors  or  long  pull 
magnets  or  solenoids,  as  the  case  may  be,  and  producing  eventually 
the  same  results  exactly  as  the  old  levers  produce.  How  the  life  of 
these  switches  will  be  affected  by  the  constant  sparking  remains  to  be 
seen,  though,  if  they  are  made  with  carbon  tips,  renewable  contacts, 
and  have  magnetic  blow-outs,  it  is  probable  that  they  will  wear  well 
and  give  but  little  trouble. 

Gas  Engines  for  Driving  Dynamos. 

I  should  like  to  have  gone  into  this  subject  in  considerable  detail, 
but  time  forbids  me  to  do  so.  The  matter  has  been  recently  dealt 
with  by  Mr.  Humphrey,  of  the  Brunner  Mond  Company,  in  a  very 
comprehensive  manner,  and  the  present  occasion  is  not  at  all  a 
suitable  one  for  an  attempt  to  vie  with  him.  One  aspect  of  the  case, 
however,  I  should  like  to  lay  before  you.  The  gas-engine  makers  of 
this  country,  who  have  turned  out  thousands  of  most  excellent 
engines,  have  for  some  years  past  had  before  them  the  object  lesson 
of  the  now  almost  universal  adoption  of  the  inverted  vertical  steam 
engine  for  driving  electric  generators.  The  demand  arose  chiefly 
from  the  fact  that  such  engines  occupy  far  less  floor  space  than  any 
other,  and  that  economy  of  floor  space  has  become  of  essential  im- 
portance. Also  that  it  is  easy  to  construct  on  that  system  three-cylinder 
engines  with  all  the  advantages  of  even  turning  moment  which  they 
possess.  The  gas-engine  makers  must  have  realised  that  eventually 
large  gas  engines  would  run  steam  engines  very  hard  economically  and 
in  other  ways,  and  notwithstanding  this  they  have  allowed  America  to 
take  the  lead  in  producing  engines  of  this  type.  Any  one  who  has  had 
to  do  with  these  engines  cannot  but  appreciate  the  straightforward 
simplicity  of  the  three-cylinder  arrangement,  the  ease  with  which  they 
are  started,  the  excellent  governing,  and  the  extremely  smooth  way  in 
which  they  run.  My  firm  has  had  the  privilege  of  engineering  a 
gas-engine  generating  plant  of,  eventually,  1,200  H.P.  at  the 
Birmingham  Small  Arms  Company's  factory,  and,  being  unable  to 
obtain  such  engines  in  Great  Britain,  we  were  obliged  to  order  them 
from  America.  So  far,  they  have  given  us  every  satisfaction,  excepting 
on  the  important  point  that  they  were  not  designed  and  built  in  our 
own  country,  which  I  must  admit  is  a  truly  saddening  consideration. 
There  is  nothing  left  for  our  own  makers  to  do  but  to  copy,  unless  it 
be,  while  following  the  type  lead,  to  produce  something  even  better 
than  the  American  engines.  Recognising  as  I  do  their  undoubted 
ability  and  skill,  I  most  sincerely  hope  that  we  may  be  within  measur- 
able distance  of.  finding  that  they  have  accomplished  such  a  highly 
desirable  result. 

Measuring  Instruments. 

Ammeters  and  voltmeters  are  the  principal  measuring  instruments 


556  LEA:   ADDRESS  AS  CHAIRMAN  [Birmingham, 

used  in  the  Electrical  Industry,  and  during  late  years  considerable 
differentiation  in  th^  types  used  for  direct-current  circuits  and 
alternating-current  circuits  has  taken  place.  Formerly  instruments 
containing  soft  iron  were  largely  used  for  both  D.C.  and  A.C.  systems. 
Now  it  is  customary  to  employ  moving  coil  instruments  in  the  former, 
and  hot  wire  or  •*  induction  "  instruments  in  the  latter.  Electrostatic 
instruments  are  used  in  both  systems,  more  especially  in  high-tension 
and  extra  high-tension  work.  The  adoption  of  moving  coil  voltmeters 
on  D.C.  circuits  has  much  to  recommend  it,  for  they  are  dead  beat, 
quick  in  action,  free  from  hysteresis  errors,  and  economical  as  regards 
power  expended  in  them.  The  same  may  be  said  of  moving  coil 
ammeters  for  currents  of  moderate  strength,  but  for  very  large  currents 
the  power  spent  in  ammeter  shunts  becomes  a  source  of  expense, 
inconvenience,  and  inaccuracy.  This  arises  from  the  fact  that  such 
ammeters  require  the  same  P.D.  to  produce  full  deflexion  whether  they 
are  for  large  or  small  currents,  and  as  this  P.D.  is  usually  about  one- 
twentieth  of  a  volt,  the  loss  in  a  shunt  for  5,000  amperes  amounts  to  a 
third  of  a  horse-power  at  full  load.  This  disadvantage  is  minimised  in 
some  cases  by  using  part  of  a  'bus-bar  or  feeder  as  the  ammeter  shunt. 
The  fact  that  only  comparatively  thin  wires  need  be  led  to  the 
indicating  instrument  is  a  great  advantage. 

For  measurements  in  which  high  accuracy  is  necessary  the  ordinary 
moving  coil  ammeter  suffers  from  temperature  errors,  owing  to  possible 
differences  in  temperatures  and  in  temperature  coefficient  of  the  shunt 
and  instrument.  Fortunately  these  errors  may  be  greatly  reduced  by 
the  use  of  Campbell's  bridge  compensating  arrangement  described  in 
his  patent  of  March,  190 1.  It  is  satisfactory  to  learn  that  Messrs. 
Elliott  Bros,  are  introducing  this  compensation  in  their  "Century" 
testing  sets.  Moving  coil  voltmeters  of  ordinary  ranges  have  little 
temperature  error,  for  they  can  be  sufficiently  ballasted  by  series 
resistance  of  negligible  temperature  coefficient. 

Hot-wire  ammeters  for  very  large  currents  are  open  to  greater 
objection,  as  regards  expenditure  of  power,  than  moving  coil  instru- 
ments, and  in  addition  to  this  they  are  slow  in  taking  up  their  steady 
readings  even  when  the  current  through  them  is  quite  constant.  This 
latter  defect  renders  the  instrument  unsuitable  for  precise  measure- 
ments in  circuits  where  the  current  fluctuates.  One  means  of  reducing 
these  defects  is  to  use  a  series  transformer  with  an  unshunted  instru- 
ment in  its  secondary  circuit. 

On  high-tension  or  extra  high-tension  systems  hot-wire  voltmeters 
when  direct-connected  arc  very  wasteful,  owing  to  a  certain  current 
being  necessary  to  cause  the  deflexion,  but  here  again  the  consumption 
of  power  can  be  lessened  by  using  step-down  transformers. 

Electrostatic  voltmeters  need  no  step-down  transformers  or  other 
pressure  changing  devices,  and  are  extremely  economical  in  power. 
They  have,  therefore,  come  into  extensive  use  in  high-pressure  stations. 
An  important  consideration  in  connection  with  alternating-current 
instruments  is  their  behaviour  under  different  conditions  of  wave-form, 
and  in  this  respect  hot-wire  and  "  induction  "  instruments  have  decided 
advantages  over  the  soft-iron  type.    As  "  induction  "  instruments  take 


1902.]  OF  BIRMINGHAM   LOCAL  SECTION.  667 

less  power  than  hot-wire  ones,  and  are  usually  more  robust,  they  are 
coming  rapidly  to  the  front. 

The  measurement  of  power  in  alternating-current  circuits  has 
attracted  considerable  attention  within  recent  years,  and  numerous 
wattmeters  have  resulted.  A  large  number  of  instruments  has  also 
recently  been  invented  to  simplify  and  expedite  the  measurement  of 
permeability  and  hysteresis  of  iron  and  steel.  The  instruments  of 
Drysdale,  Searle  and  Hoiden  are  perhaps  the  most  novel  of  these 
productions.  It  is  to  be  hoped  that  these  contrivances  will  induce 
users  of  iron  and  steel  for  magnetic  purposes  to  test  consignments 
themselves. 

Within  my  four  years  period,  one  instrument  has  been  brought  out 
which,  to  my  mind,  is  the  most  interesting  that  has  been  devised 
for  many  years,  and  is  well  worth  our  attention  for  a  short  time.  I 
refer  to  Mr.  DuddelFs  oscillograph.  My  admiration  of  it  must  be  my 
excuse  for  bringing  it  alone  before  you  this  evening.  Through  the 
courtesy  of  Mr.  Duddell  I  am  able  to  show  you  the  instrument  in 
operation,  and  I  am  very  much  indebted  to  Mr.  Duddell  for  the  loan  of 
the  instrument,  and  to  him  and  the  sta£E  of  the  Electrical  Engineering 
Department  of  this  University  for  the  trouble  which  they  have  taken  in 
setting  up  the  instrument  and  all  the  accessories  on  this  occasion. 

At  the  end  of  the  Chairman's  address  a  demonstration  was  given, 
showing  the  capabilities  of  the  Duddell  Oscillograph.  The  experi- 
ments were  conducted  by  Mr.  Duddell  himself. 


658  EARLE:    ADDRESS  AS   CHAIRMAN  [Manchester, 

MANCHESTER    LOCAL    SECTION. 


INAUGURAL  ADDRESS   OF  CHAIRMAN, 
By  Mr.  H.  A.  Earle,  Member. 

{ABSTRACT.) 

{Address  delivered  January  20,  1903.) 

It  is  with  pleasure  that  I  avail  myself  of  this  opportunity  to  express 
my  thanks  to  you,  who,  as  members  of  the  Institution  of  Electrical 
Engineers  representing  the  Manchester  Section,  have  paid  me  the 
compliment  of  electing  me  your  Chairman  for  the  present  session.  It 
is  a  compliment  which  I  greatly  appreciate.  The  growing  importance 
of  the  Manchester  Section  of  the  Institution  is  most  opportune  at  a  time 
when  the  electrical  industry  is  making  rapid  and  important  strides  here. 
As  a  centre  for  electrical  works  in  this  country,  Manchester  and  district 
is  now  the  largest  and  most  important.  Moreover,  Lancashire  and  the 
neighbouring  county  of  Yorkshire  will,  within  a  comparatively  short 
period,  possess  electrical  generating  stations  which  will  be  second  to 
none  in  the  country  as  regards  either  size  or  importance.  Besides  the 
large  municipal  supplies  in  Manchester,  Liverpool,  and  other  towns 
the  Lancashire  and  the  Yorkshire  Power  Companies  will  shortly  start 
operations;  and,  notwithstanding  the  progress  of  the  past,  we  may 
confidently  anticipate  a  development  in  the  future  which  will  surpass 
anything  we  have  witnessed. 

With  regard  to  progress  in  the  past,  those  who  have  been 
associated  with  Electrical  Engineering  during  the  last  twenty  years 
have  witnessed  a  development  and  application  which  the  most  sanguine 
could  hardly  have  anticipated.  Within  the  period  named  the  investiga- 
tions, inventions,  and  developments  which  have  chiefly  contributed  to 
the  advancement  of  the  industry  are  : — 

The  production  and  commercial  manufacture  of  the  high-voltage 

incandescent  lamp. 
The  mathematical  treatment  of  the  fundamental  principles  of  the 

electric  generator. 
Tlie  three-wire  system. 

The  series-parallel  control  for  traction  work,  and 
The  induction  motor. 

When  mentioning  high-voltage  lamps,  I  do  not  especially  refer  to 
the  modern  lamps  of  200  volts  and  upwards^ut  to  the  invention  and 
development  of  lamps  with  carbon  filaments. 

The  mathematical  treatment  of  the  principles  of  the  dynamo,  and 
the  laws  which  were  thereby  laid  down  for  its  construction,  was  the 
most  important  contribution  to  the  problem  of  electrical  engineering 
which  has  been  made. 


1903.]  OF   MANCHESTER   LOCAL  SECTION.  559 

By  no  means  one  of  the  least  important  points  in  the  evolution  of 
the  generator  is  the  universal  adoption  of  carbon  brushes,  which  has  so 
greatly  assisted  to  sparkless  running  and  fixed  lead.  Various  qualities* 
of  carbon  have  been  introduced  of  different  resistance  and  hardness  ; 
those  of  higher  resistance  and  finer  grain  being  found  most  suitable  for 
high-potential,  and  those  of  low  resistance  and  coarser  grain  for  low- 
potential  machines,  for,  as  a  rule,  no  one  type  of  carbon  is  found  equally 
suitable  for  a  large  range  or  variety  of  generators. 

Incidentally  the  development  of  the  electrical  generator  gave  a 
strong  impetus  to  the  improvement  of  the  steam  engine,  and  the  great 
accuracy  with  which  electrical  measurements  can  be  carried  out  has 
been  the  means  of  enabling  the  steam  consumption  at  all  loads  to  be 
definitely  ascertained,  and  one  type  of  engine  to  be  readily  compared 
with  another.  This  has  led  to  the  acquisition  of  much  useful  knowledge, 
and  to  many  improvements  in  design. 

By  the  adoption  of  the  three-wire  system  in  place  of  a  two-wire 
circuit,  the  weight  of  the  copper  required  to  transmit  a  given  power  a 
stated  distance,  with  the  same  percentage  of  loss,  has  been  very  much 
reduced,  and  during  the  last  few  years  the  introduction  of  incandescent 
lamps  for  double  the  previous  voltage  has  extended  the  scope  of  supply 
on  the  three-wire  system  to  such  an  extent  that  direct-current  supply 
has  received  a  new  lease  of  life,  and  the  competition  which  at  one  time 
existed  in  this  country  with  the  single-phase  system  has  been  to  a  great 
extent,  if  not  entirely,  eliminated. 

The  series-parallel  control  for  tramway  work  was  one  of  the  great 
steps  which  placed  electric  traction  upon  a  sound  commercial  footing. 
By  its  adoption  the  units  per  car-mile  were  reduced  by  some  30  per  cent., 
and  the  maximum  current  demanded  from  the  station  by  approximately 
the  same  amount,  and  the  great  reduction  that  this  represented  in  the 
first  cost  of  the  generating  station  and  in  the  cost  per  car-mile  is  well 
known  to  all  engineers. 

The  induction  motor,  and  the  branch  of  electrical  engineering  to 
which  it  is  alUed,  is  the  present  day  development  of  the  alternating- 
current  systems.  For  many  reasons  three-phase  machines  have  not 
been  so  largely  adopted  in  this  country  as  in  some  others.  The 
increasing  size  of  stations  and  the  increasing  need  for  placing  them 
further  out  has,  however,  given  rise  to  an  increasing  demand  in  this 
country  for  polyphase  currents.  But  there  is  no  rivalry  between  the 
direct  and  polyphase  systems ;  each  has  its  proper  place. 

A  review,  however  superficial  and  short,  of  past  progress  may  well 
cause  us  to  ask  what  degree  of  perfection  have  we  arrived  at,  and  what 
may  we  anticipate  for  the  future  ?  New  discoveries  and  developments 
generally  tend  to  simplification,  and  the  operations  by  which  a  given 
purpose  is  effected  are  generally  reduced  in  number  as  experience  is 
gained  and  as  the  problem  dealt  with  is  better  understood.  If  this 
could  in  any  way  be  accepted  as  a  law,  a  brief  consideration  of  the 
pwesent  method  of  generating  light  would  indeed  prove  that  our 
procedure  is  most  primitive ;  for  it  is  evident,  even  to  the  most 
uninitiated,  that  we  obtain  our  light  by  an  exceedingly  roundabout 
process,  and  that  being  so,  we  cannot  expect  that  it  should  be  highly 


660  EARLE:    ADDRESS  AS  CHAIRMAN         [Manchester, 

efficient  or  economical.    A  brief  consideration  will  show  the  result 
which  is  attained. 

•  Taking  coal  having  a  calorific  value  of  14,500  units  per  pound,  and 
assuming  9  lbs.  of  steam  to  be  evaporated  to  160  lbs.  pressure  per 
pound  of  fuel,  the  efficiency  of  the  boiler  and  cconomiser  is,  approxi- 
mately, 72  per  cent.  An  engine  taking  13  lbs.  of  steam  per  I.H.P.  has 
an  efficiency  of  about  17  per  cent.,  or  a  combined  efficiency  with  the 
boiler  of  approximately  12  per  cent. ;  and,  assuming  the  ratio  of  the 
B.H.P.  to  the  indicated  power  of  the  engine  to  be  90  per  cent.,  we  find 
that  the  ratio  of  the  useful  return  in  B.H.P.  to  the  heat  units  in  the  coal 
is  represented  by  107  per  cent.  Now  7  per  cent,  of  this  figure  is  lost 
in  the  generator,  giving  an  efficiency  of  E.H.P.  coal  burned  of  10  per 
cent 

The  heat  units  in  the  coal  have  been  very  inefficiently  utilised,  but 
what  happens  during  the  operation  of  converting  electrical  energy  into 
light  ?  From  investigations  which  have  been  made  in  connection  with 
the  energy  consumed  by  an  incandescent  lamp,  it  has  been  shown  that 
only  a  small  portion  of  the  total  radiation  is  luminous  and  capable  of 
a£Fecting  the  eye  as  light.  Taking  this  portion  as  5  per  cent  on  the 
average,  we  find  that  of  the  total  heat  units  in  the  coal  practically  the 
whole  are  dissipated,  and  only  a  remainder  of  ^  per  cent,  is  converted 
into  the  light  which  it  has  been  our  object  to  produce. 

This  small  result  obtained  in  return  for  so  much  coal  burned  is  most 
unsatisfactory,  but  how  are  matters  to  be  bettered,  and  from  whence  is 
improvement  to  come  ? 

It  is  evident  that  for  the  cheaper  production  of  light  by  means  of 
the  incandescent  lamp  we  must  look  to  improvement  in  the  lamp  itself, 
for  it  is  the  most  inefficient  member  of  the  system  with  which  we  have 
to  deal,  and  since  its  introduction  but  little  appreciable  advance  has 
been  made  in  its  efficiency.  The  production  of  light  by  the  arc  gives 
a  somewhat  better  return,  the  ratio  of  luminous  to  total  radiation  being 
between  5  per  cent,  and  15  per  cent,  and  the  useful  return  from  the 
heat  units  in  the  coal  burnt  about  i  per  cent. 

When  electrical  energy  is  required  for  the  production  of  power, 
owing  to  the  high  efficiency  of  the  electric  motor,  which  is  between 
90  and  95  per  cent,  according  to  size,  a  net  return  of  nearly  10  per  cent, 
is  obtained,  and  in  this  case  the  greatest  loss  takes  place  in  the  steam 
engine. 

Besides  the  study  of  the  efficiency  of  engines,  generators,  lamps, 
and  motors,  there  is  in  connection  with  our  present  generating  stations 
an  item  amongst  the  expenses,  which  all  who  analyse  the  published 
returns  well  know  varies  between  wide  limits,  and  this  is  the  cost  of 
fuel  per  unit  generated.  It  might  possibly  be  thought  that  these  large 
differences  were  chiefly  due  to  the  price  per  ton  which  has  to  be  paid, 
but  investigation  will  show  that,  apart  from  any  question  of  price,  the 
actual  pounds  of  fuel  burnt  per  unit  sold  or  generated  vary  widely  at 
different  stations,  even  though  the  quality  of  the  coal  may  not  vary 
greatly  and  the  load  factor  may  be  very  similar. 

The  type  and  size  of  engine,  the  class  of  boiler,  the  load  factor,  and 
the  nature  of  the  load,  account  for  a  great  portion  of  this  difference. 


Ito3.]  OF  MANCHESTER  LOCAL  SECTION.  661 

but  it  seems  more  than  probable  that  there  is,  in  many  instances,  a 
large  personal  element  involved. 

Electrical  generating  stations  for  lighting  and  traction  have  for 
some  time  been  laid  down  on  lines  which  have  varied  but  little.  There 
is,  however,  a  great  development  before  us.  Large  power-stations  are 
about  to  be  erected  in  various  parts  of  the  country  to  supply  power 
over  large  areas,  and  many  of  the  larger  towns  are  building,  or  are 
about  to  build,  very  large  generating  stations.  All  those  connected 
with  these  undertakings  are  naturally  only  too  ready  to  take  advantage 
of  any  new  development,  improvement,  or  invention  which  may  assist 
to  further  economies.  Are  any  such  opportunities  offered  to  us  ?  Is 
there  any  probability  of  the  present  reciprocating  steam  engine  being 
superseded,  or  can  we  look  for  improvement  in  the  incandescent  lamp, 
which,  owing  to  its  present  low  cfi&ciency,  is  the  most  unsatisfactory 
member  of  our  lighting  system  ? 

With  regard  to  the  former,  two  types  of  engines  are  now  forcing 
themselves  upon  our  notice.  They  are  the  steam  turbine  and  the  gas 
engine. 

The  steam  turbine,  in  the  able  hands  of  its  inventor,  is  now  reaching 
a  degree  of  perfection  when  it  can  no  longer  be  neglected,  for  it  is  not 
only  becoming  the  rival  of,  but  for  many  purposes  is  actually  threaten- 
ing to  supersede,  the  reciprocating  engine.  An  engine  in  which  the 
moving  parts  are  reduced  to  the  miniinum  cannot  fail  to  be  attractive, 
and  in  the  turbine,  valves,  eccentrics,  and  reciprocating  parts  are  entirely 
absent.  The  economies  which  have  been  effected  in  the  steam  con- 
sumption of  the  turbine  are  due  to  a  variety  of  improvements,  but  to  a 
large  extent  to  the  advances  which  have  been  made  in  connection  with 
it  when  running  condensing.  The  design  of  the  turbine  constitutes  it 
a  multiple-expansion  engine,  in  which  the  steam  can  be  expanded  one 
hundred-  or  even  two  hundred-fold,  as  compared  with  eight-  to  sixteen- 
fold  in  the  compound  or  triple-expansion  reciprocating  engine.  To 
this  exceptional  ratio  of  expansion  the  economy  of  the  engine  is  to  a 
large  extent  due,  and  as  the  expansion  extends  over  nearly  the  whole 
range  between  the  boiler  pressure  and  that  in  the  condenser,  the  effect 
of  a  good  vacuum  is  most  important,  and  for  every  additional  inch  of 
vacuum  above  25  to  26  a  saving  of  approximately  5  per  cent,  is  obtained. 
In  the  turbine  there  is  no  initial  condensation,  and  therefore  greater 
gain  by  a  good  vacuum  than  in  the  reciprocating  engine.  In  the  latter 
type  of  engine  a  function  of  good  vacuum  is  a  corresponding  increase 
of  size  of  the  engine  so  as  to  cope  with  the  greater  volume  of  steam, 
but  this  is  not  so  in  the  turbine,  and  on  this  account;  in  the  turbine, 
steam  can  be  expanded  to  a  limit  which  mechanical  considerations 
render  impermissible  in  the  reciprocating  engine.  In  the  average 
reciprocating  engine  much  loss  is  caused  year  in  and  year  out  by  leaky 
slide  valves,  and  great  loss  is  due  to  alternate  contact  of  the  inside  of 
the  cylinder  walls  with  cold  exhaust  and  hot  steam  ;  but  in  turbines,  as 
the  flow  is  always  in  one  direction,  there  are  no  periodic  fluctuations, 
and  therefore  none  of  the  above  loss.  Besides  the  excellent  results  as 
regards  steam  consumption  in  the  turbine,  it  claims  other  advantages 
of  considerable  importance.    The  first  cost  of  the  combined  plant  is 


662  EARLE:    ADDRESS  AS  CHAIRMAN         [Manchester. 

appreciably  reduced,  the  necessary  buildings  are  much  smaller,  and 
the  foundations  inexpensive.  No  internal  lubrication  is  necessary — the 
saving  on  this  account  is  considerable — and  the  condensed  steam  can 
be  returned  to  the  boiler  uncontaminated  by  oil,  and  without  the 
necessity  for  oil  filters. 

The  second  type  of  engine,  viz.,  that  using  gas  as  the  motive  power, 
has  comparatively  recently,  owing  to  the  greatly  increased  size  in  which 
it  can  now  be  built,  and  the  production  by  various  processes  of  cheap 
gas,  won  for  itself  a  very  high  position,  and  one  which  is  fully  justified 
by  its  performances,  and  it  has  established  its  claim  as  a  competitor  of 
the  best  and  largest  steam  engines. 

The  four  strokes  per  cycle  single-acting  engine  is  that  which  in  the 
past  has  been  commercially  the  most  successful,  but  as  the  demand  for 
engines  of  larger  and  larger  size  has  arisen,  the  disadvantage  of  only 
utilising  one  stroke  in  every  four  for  the  generation  of  power,  and  the 
necessity  for  two  or  even  four  cylinders  for  engines  of  no  very  great 
power  is  tending  rather  to  the  adoption  of  one  impulse  per  revolution, 
or  even  one  impulse  per  stroke. 

Records  exist  in  great  quantity  of  gas  engine  performances,  both 
for  the  older  and  more  modern  types,  but  it  is  unfortunate  that  con- 
fusion should  be  so  often  caused  in  their  study  by  the  envployment 
of  units  based  on  different  temperature  scales  and  weights.  Thermal 
efficiencies  are  also  calculated  in  two  different  manners,  based  either 
upon  the  higher  or  the  lower  value  of  the  gas,  and  by  the  existence 
of  three  determinations  of  calorific  value,  and  two  methods  of  cal- 
culating the  thermal  efficiency,  the  performance  of  an  engine  may 
be  presented  to  us  in  any  of  six  ways.  This  in  an  outrage  upon  our 
time  and  patience,  more  especially  when  one  has  frequently  to  search 
through  a  whole  book  or  paper  to  discover  the  units  upon  which  the 
results  are  based. 

So  long  as  gas  engines  were  run  upon  town  gas  their  field  of  opera- 
tions was  limited  to  comparatively  small  powers.  But  as  the  size  of 
engines  increases,  the  efficiency  of  the  steam  engine  rapidly  improves, 
while  for  the  gas  engine  it  remains  more  nearly  constant ;  consequently 
the  utilisation  of  high-priced  illuminating  gas  does  not  admit  of 
economical  working  except  for  small  powers.  To  enable  gas  engines 
to  compete  with  steam  for  the  generation  of  power  on  a  large  scale, 
a  cheap  and  reliable  gas  is  essential,  and  for  many  years  inventors 
have  been  working  on  this  most  interesting  and  important  problem. 
Apart  from  the  question  of  producers,  designed  especially  for  the 
manufacture  of  'power  gas,  there  are  sources  of  supply  which,  when 
available  and  turned  to  account,  yield  exceedingly  valuable  results, 
and  the  utilisation  of  the  gases  from  blast  furnaces  and  coke  ovens — 
the  great  portion  of  which  has  up  to  the  present  been  allowed  to  go  to 
waste — is  a  problem  of  the  very  greatest  importance. 

Excluding  illuminating  gas,  which  is  too  expensive  for  use  in  large 
gas  engines,  natural  gas,  blast  furnace  and  coke  oven  gases,  which  are 
only  occasionally  available,  three  kinds  of  gas  remain,  which  are  named 
respectively  producer,  water,  and  power  gas. 

Producer  gas  is  generated   by  forcing  a  current  of   air   through 


1903]  OF   MANCHESTER  LOCAL  SECTION.  663 

glowing  coal.  Water  gas  is  produced  by  passing  steam  through  fuel 
which  has  been  raised  to  incandescence  by  first  passing  a  current 
of  air  through  it.  The  production  of  power  gas  is  a  combination 
of  the  two  processes,  in  which  steam  and  air  are  admitted  simul- 
taneously, and  though  the  resultant  gas  is  poorer  in  quality  than  water 
gas  it  is  richer  than  producer  gas,  and  the  process  has  the  great  advan- 
tage of  being  a  continuous  one. 

Power  gas  was,  during  the  early  years  of  its  manufacture,  made 
from  anthracite  or  coke,  and  excellent  results  have  been  obtained,  by 
which  a  horse-powcr-hour  is  produced  for  about  i  lb.  of  coal,  but  lately 
a  process  has  been  designed  which  enables  the  cheapest  bituminous 
coal  and  slack  to  be  used  and  at  the  same  time  the  ammonia  to  be 
recovered  as  sulphate  of  ammonia.  It  is  hardly  to  be  wondered  at  that 
this  great  advance  in  the  economical  production  of  gas  has  brought  the 
question  of  the  utilisation  of  gas  engines  for  the  production  of  power 
on  a  large  scale  into  great  prominence. 

The  relative  working  costs  of  gas-  and  steam-driven  plants  are 
dependent  upon  the  quality  and  cost  of  fuel  which  the  type  of  pro- 
ducer requires,  and  the  cost  of  coal  for  the  steam  plant. 

Briefly  comparing  a  400- H. P.  steam  plant  with  a  gas  plant  of  equal 
power  (the  latter  utilising  gas  manufactured  from  anthracite),  we  find 
that  a  400- H. P.  compound  steam  engine,  condensing,  including  boilers, 
boiler-house  and  chimney.,  would  involve  a  capital  outlay  of  approxi- 
mately ;£ 5,900.  When  working  this  plant  for  3,000  hours  per  annum, 
and  taking  the  cost  of  coal  at  los.  per  ton,  the  total  yearly  cost,  in- 
cluding depreciation  and  interest  on  capital,  would  be  £ifS7S'  This 
gives  a  cost  per  H.P.  per  hour  of  0*325  pence. 

Considering  this  against  a  gas  engine,  producer,  and  building,  the 
total  capital  outlay  for  the  plant  for  the  utilisation  of  anthracite  would 
be  ;£4,5oo,  and,  taking  the  anthracite  at  23s.  per  ton,  the  working 
expenses  would  be  ;£i475,  or  03  pence  per  H.P.  hour. 

These  figures  relate  to  a  plant  in  which  expensive  fuel  is  used  in  the 
producer,  and  when  considering  the  cost  per  H.P.-hour  it  must  be 
borne  in  mind  that  it  is  assumed  the  plants  are  running  for  ten  hours 
per  day  on  full  load. 

With  respect  to  producers  for  the  production  of  gas  from  bitu- 
minous slack,  the  cheaper  fuel  gives  results  which  show  a  considerable 
economy  when  gas  plants  of  even  500  H.P.  are  compared  with  steam, 
and  without  taking  into  account  the  question  of  ammonia  recovery. 
But  when  the  power  rises  to  3,000  H.P.,  or  thereabouts,  and  it  becomes 
economically  advantageous  to  recover  the  ammonia,  the  value  of  this 
bye-product  reduces  the  nett  cost  of  the  gas  to  such  a  figure  that,  with 
coal  delivered  at  8s.  a  ton,  the  nett  cost  of  fuel  does  not  exceed  one- 
twentieth  of  a  penny  per  H.P.-hour.  Such  a  result  is  one  which  points 
to  the  certainty  of  the  adoption  of  the  gas  engine  for  all  large  power 
plants. 

Besides  the  reduction  of  coal  consumption  by  the  aid  of  rotary 
steam  engines  or  of  gas  engines,  there  is  the  possibility  of  reducing 
the  cost  per  unit  by  improving  the  load  factor.  A  large  generating 
station,  with  a  tramway  and  power  load  may  have  a  factor  approxi- 


564  EARLE:    ADDRESS  AS  CHAIRMAN         [Manchester, 

mating  to  20  per  cent.  If  this  could  be  increased  to  50  per  cent.,  costs 
would  fall  by  practically  one-half.  Storage  batteries  are  the  only  known 
means  at  our  disposal  for  effecting  an  immediate  change  of  this  mag- 
nitude ;  large  first-cost  and  the  maintenance  charges  alone  stand  in 
the  way  of  their  immediate  adoption  upon  an  enormous  scale.  We 
are,  in  fact,  waiting  for  the  ideal  storage  battery.  The  destruction 
of  storage  batteries  is  due  to  the  continual  expansion  and  contraction. 
A  cell  with  a  life  greatly  in  excess  of  anything  yet  produced  is  no 
impossibility.  Whether  the  iron,  nickel-oxide  battery,  of  which  we 
have  heard,  is  to  solve  the  problem  of  long  life,  or  whether  iron  is  to 
replace  lead,  I  do  not  know  ;  but  iron  is  the  cheapest  of  metals,  and, 
weight  for  weight,  should  yield  a  watt-hour  output  about  the  same 
as  zinc,  and  many  times  greater  than  lead,  and  if  the  initial  difficulties 
have  been  overcome  this  new  departure  in  batteries  will  be  of  the  first 
importance.  But  it  is  well  to  note  that  a  great  length  of  life  is  not  all 
that  is  required,  the  first  cost  being  as  important  a  factor,  for  the 
interest  on  any  additional  outlay  must  be  charged  against  any  saving 
effected  in  yearly  depreciation ;  and,  if  the  cost  of  the  battery  is 
increased,  in  order  that  the  yearly  charges  shall  remain  constant,  the 
life  must  increase  as  the  square  of  the  cost.  Apart,  however,  from  the 
use  of  batteries  merely  for  the  purp>ose  of  storage,  there  is  an  immense 
field  for  their  employment  as  regulators  in  large  power-stations. 

Touching  upon  the  question  of  •the  supply  of  electricity  in  bulk  for 
power  and  other  purposes,  this  is  a  subject  upon  which  a  war  of  argu- 
ment has  been  waged,  and  the  financial  success  of  such  undertakings 
has  been  questioned.  We  may,  however,  leave  this  great  question  to 
decide  itself  upon  its  merits,  for  several  of  the  power  companies  have 
already  started  operations.  The  power  companies  have  been  excluded 
from  giving  customers  a  supply  within  certain  town  areas,  with  the 
object  of  protecting  the  municipalities  from  competition,  and  although 
the  towns  are  at  liberty  to  take  a  supply,  or  give  permission  to  supply, 
they  as  a  rule  do  not  at  present  look  with  favour  upon  these  gentlemen 
with  roving  commissions.  Still,  the  effect  of  the  companies,  carrying 
on  operations  outside  their  gates,  will  be  felt,  for  low  charges  for  power 
will  tend  to  attract  small  manufacturing  firms  to  districts  where  rates 
are  low  and  land  is  cheap. 

I  have  given  some  consideration  to  the  question  of  the  supply  of 
energy  by  power  companies  for  the  purpose  of  lighting  small  districts, 
and  have  also  worked  out  the  savings  that  would  be  effected  and  the 
extra  expenses  that  would  be  entailed  by  putting  in  batteries  of 
sufficient  size  to  increase  the  load  factors  from  9  per  cent,  to  20  per 
cent.,  and  the  result  of  my  investigations  goes  to  show  that  the  prices 
which  would  have  to  be  charged  compare  most  favourably  with  those 
charged  by  small  companies  having  outputs  similar  to  those  I  have 
assumed.  But  the  true  object  of  the  power  companies  is  the  supply 
of  energy  for  power,  and  for  success  upon  a  large  scale  all  costs  must 
be  cut  down  to  the  lowest  possible  figure.  Hence  such  companies  are 
bound  to  give,  as  I  have  said  before,  consideration  to  the  steam  turbine, 
the  gas  engine,  etc.  The  cost  of  the  electric  light  could  also  be  reduced 
by  improvements  in  the  lamp  itself.    At  the  present  time  the  efficiency 


1903.]  OF  MANCHESTER  LOCAL   SECTION.  566 

of  the  lamp  is  such  that  the  hourly  cost  of  current  greatly  exceeds  the 
hourly  cost  of  the  lamp,  for,  taking  the  cost  of  a  60- watt  lamp  at  is. 
and  its  useful  life  at  1,000  hours,  we  find  that  at  4d.  per  unit  the  hourly 
cost  of  current  amounts  to  twenty  times  the  hourly  cost  of  the  lamp. 
This  great  difference  between  the  two  charges  indicates  that  the  lamp 
should,  on  commercial  considerations,  be  called  upon  to  do  more  work 
with  a  smaller  expenditure  of  power,  even  if  thereby  its  Hfe  were 
shortened.  Many  attempts  have,  of  course,  been  made  to  produce 
a  substance  capable  of  being  run  at  a  higher  temperature  than  carbon, 
and  there  is  no  reason  why  we  should  not  look  forward  to  an  efficiency 
which  would  at  any  rate  halve,  or  even  quarter,  the  present  cost  of 
lighting.  The  mercury  lamp  may  indicate  the  type  of  the  future,  but 
at  present  the  quality  of  its  light  is  not  such  as  would  recommend  its 
adoption. 

And  now  to  what  extent  are  our  home  firms  in  a  position  to  take 
advantage  of  home  and  colonial  demand.  I  am  convinced  that  we  are 
in  every  way  able  to  hold  our  own  in  the  competition,  but  we  must  not 
fall  into  the  dangerous  error  of  hiding  from  ourselves  the  many 
excellent  features  in  the  machinery  of  our  foreign  rivals.  Looking 
back  upon  the  steady  and  continual  progress  which  has  been  made, 
and  considering  the  great  opportunities  that  are  still  open  for  improve- 
ments in  the  various  branches  of  electrical  engineering,  the  many 
applications  of  electricity  which  are  only  yet  partially  developed, 
and  its  great  future  in  connection  with  power-distribution  and  electro- 
chemistry, one  cannot  help  feeling  with  some  degree  of  confidence 
that  the  progress  of  the  present  century  wilt  equal,  if  not  surpass, 
that  of  the  last. 


566  DICKINSON  :*  ADDRESS   AS   CHAIRMAN  [I^ds, 

LEEDS  LOCAL   SECTION. 


INAUGURAL  ADDRESS   OF  CHAIRMAN, 
By  Mr.  HAROLD  Dickinson,  Member. 

(ABSTRACT.) 
{Address  delivered  February  jqth^  ^903.) 

In  electing  me  your  chairman  for  the  first  year  of  the  existence  of 
the  Leeds  Section  of  the  Institution  of  Electrical  Engineers,  you  have 
conferred  on  me  an  honour  of  which  I  am  justly  proud,  and  for  which 
I  thank  you. 

In  the  earlier  part  of  my  address  I  propose  briefly  to  rehearse  the 
objects  and  advantages  of  the  Institution,  and  with  regard  to  the  rest  of 
my  remarks  I  have  decided,  after  some  thought,  to  leave  all  technical 
matter  to  be  dealt  with  in  papers  specially  devoted  to  specific  subjects 
and  to  seek  to  lay  before  you  the  commercial  and  educational  problems 
with  which,  sooner  or  later,  we  shall  have  to  deal.  This  I  do  in  no  dog- 
matic spirit,  but  rather  in  the  hope  that,  by  pointing  out  what  I  conceive 
to  be  imperial  issues,  an  avenue  is  opened  for  their  consideration  and 
discussion. 

The  Institution  of  Electrical  Engineers  was  founded  in  187 1  under 
the  title  of  the  Society  of  Telegraph  Engineers.  It  is  the  oldest  and 
largest  Institution  of  electriqal  engineers  in  the  world.  The  Institution 
has  not  only  grown  rapidly  in  membership,  but  it  has  grown  in  its  utilit>\ 
Local  Sections  have  been  formed  at  home  and  abroad.  Science  Abstracts 
have  been  circulated.  Visits  have  been  paid  to  foreign  countries  and 
capitals — to  Switzerland  in  1899,  to  Paris  in  1900,  to  Berlin  in  1901,  and 
one  will  be  paid  to  Italy  this  year,  and  another  to  America  next  year. 
The  Institution  has  also  exercised  its  influence  in  regard  to  Board  of 
Trade  Regulations,  Factory  Acts,  and  so  forth. 

I  have  indicated  some  of  the  lines  on  which  the  Institution  has 
moved  in  the  past,  but  there  are  other  duties  that  will  be  expected  of  it 
in  the  future.  The  competition  from  foreign  nations  now  being  experi- 
enced in  the  electrical  industry  necessitates  the  careful  attention  of  the 
Institution  to  all  the  problems  relating  to  the  progress  of  the  industry, 
which  I  hope  soon  to  see  having  serious  consideration,  such  as  questions 
of  the  management  and  conditions  of  workshops,  conditions  of  labour, 
education  and  fiscal  conditions.  These  questions  necessarily  cannot  be 
discussed  by  an  Institution  of  this  kind  with  any  view  to  interference, 
but  purely  so  that  the  best  methods  may  be  brought  to  the  notice 
of  the  manufacturers  themselves  and  the  representatives  of  labour,  edu- 
cation, and  the  public  at  large.  Then  the  Institution  may,  through  its 
influence  with  the  Colonies,  be  able  to  promote  the  interest  of  the 
industry  by  making  known  to  its  Lo^aJ  Sections  all  that  is  going  on  at 


1903.]  OF   LEEDS   LOCAL  SECTION.  667 

home  and  abroad.  Further,  the  conviction  I  believe  the  Colonies  have 
that  the  electrical  industry  at  home  is  in  a  worse  state  than  actually  is  the 
case,  can  easily  be  corrected  through  their  own  Sections. 

As  to  the  origin  of  our  Local  Section,  I  may  remind  you  that  it  was 
some  nineteen  years  ago  that  the  first  efforts  were  made  to  form  an 
Electrical  Engineering  Society  in  Yorkshire.  The  movement,  however, 
fell  through.  Through  the  instrumentality  of  our  Hon.  Sec,  Mr.  G.  R. 
Blackburn,  a  local  society  has  now  become  an  accomplished  fact  by 
the  formation  of  the  Leeds  Section. 

I  should  like  to  point  out,  now  the  Section  is  in  existence,  that  the 
responsibility  of  members  does  not  end  with  the  payment  of  the  annual 
subscription,  and  that,  in  order  to  make  the  Section  a  success,  it  is 
necessary  each  member  should  take  a  keen  interest  in  the  work.  I  find 
that  the  membership  of  the  various  Local  Sections  is  as  follows  :  Man- 
chester 445,  Leeds  i8i,  Birmingham  i8o,  Glasgow  175,  Newcastle  140, 
Dublin  65.  It  will  be  seen,  therefore,  that  with  regard  to  member- 
ship, as  compared  with  other  Local  Sections,  we  are  very  well  off,  and 
it  only  remains  for  the  members  to  put  in  a  little  of  the  enthusiasm  they 
instil  into  their  profession  to  make  this  Section  one  of  which  the  parent 
Institution  and  the  other  sections  will  be  proud. 

Before  coming  to  the  immediate  subject  of  the  second  part  of  my 
address,  I  should  like  to  call  your  attention  to  the  phenomenal  progress 
which  the  industry  in  which  we  are  all  interested  has  made  during  the 
last  thirty  years.  In  the  early  days  Telegraphy  was  its  mainstay,  then 
came  Telephony,  then  Lighting,  and  then  Traction,  in  which  there  is  now 
;£6o,ooo,ooo  of  capital  invested.  In  regard  to  lighting,  the  enlargement 
of  the  business  has  enabled  the  cost  of  production  to  be  reduced,  and 
we  may  anticipate  further  reductions  in  the  near  future  by  reason  of  the 
improvement  in  the  load-factors  due  to  a  more  diversified  type  of  user. 
The  price  at  which  electrical  energy  can  even  now  be  sold  is  such  as  to 
place  it  within  the  reach  of  all  classes. 

One  great  reason  why  there  is  not  a  much  greater  increase  is,  I 
think,  the  initial  cost  of  wiring.  Any  steps  taken  to  reduce  this  cost 
must  tend  to  the  benefit  of  the  business  and  lead  to  an  increased  use  of 
electric  light  as  an  illuminant. 

We  have  all  recently  heard  a  great  deal  about  the  various  power 
schemes  that  have  been  formulated  throughout  the  country.  It  seems 
to  have  been  assumed  by  many  people  that  because  a  scheme  is 
designated  a  power  scheme  it  possesses  some  merit  which  will  enable 
power  to  be  supplied  at  very  low  cost,  but  the  principles  which  go 
towards  the  production  of  energy  at  low  cost  are  apparently  forgotten. 
Unless  a  power  scheme  has  a  good  load  factor  it  seems  hopeless  to 
expect  low  costs,  yet  in  many  of  these  cases  the  areas  are  immense  and 
the  districts  very  scattered,  which  involve  very  heavy  distribution 
costs.  I  do  not  wish  to  say  one  word  to  discourage  any  scheme  which 
may  benefit  the  industry,  but  I  consider  that,  before  the  public  are 
invited  to  subscribe  money  for  the  development  of  some  of  the 
schemes  proposed,  the  facts  should  be  very  carefully  weighed  in  the 
light  of  our  present  experience  of  the  factors  which  govern  the  cheap 
production  of  power,  for,  if  a  number  of  these  schemes  are  unsuccess- 

YoL.  82.  88 


568  DICKINSON:  ADDRESS  AS  CHAIRMAN  [Leeds, 

ful,  it  will  tend  to  shake  the  confidence  of  investors  and  thereby  cause 
a  serious  check  to  the  industry. 

What  has  already  been  stated  shows  very  briefly  how  the  industry 
has  advanced,  and  its  continued  advancement  may  be  forecast 
when  we  consider  the  number  of  new  schemes  for  the  future. 

Our  Position  to  meet  Competition. 

But,  gentlemen,  the  consideration  we  have  just  given  to  the 
development  and  prospects  of  the  industry  at  once  suggests  the 
question,  ''To  what  extent  are  we  equipped  for  meeting  the  future, 
electrically  and  generally  ? " 

It  will  be  admitted  that  commerce  plays  a  very  important  part  in 
deciding  the  position  that  a  country  occupies  among  the  nations  of  the 
world,  and,  true  as  this  is  of  our  day,  how  much  more  so  is  it  of  the 
future  ?  We  must  all  appreciate  this,  and  it  is  therefore  incumbent  on 
us  as  a  nation  to  study  commerce  and  all  things  that  tend  to  enlarge 
and  foster  it.  There  are,  of  course,  many  avenues  through  which  we 
may  study  it,  and  this  brings  me  to  the  crux  of  my  address,  and, 
conscious  as  I  am  of  my  own  limitations,  I  only  deal  with  the  subject 
because  I  feel  that  the  position  of  commerce  generally,  and  the  electrical 
industry  in  particular,  in  the  United  Kingdom  is  not  on  the  sound  basis 
we  should  all  like  to  see  it.  The  question  before  us  is  of  vital 
importance  both  to  the  producer  and  the  user  of  electrical  apparatus. 
The  magnitude  of  the  problem  is  obvious,  and  I  fully  appreciate  the 
vast  knowledge  essential  in  order  to  arrive  at  a  correct  decision  as  well 
as  my  own  lack  of  that  wide  experience  necessary  for  the  formation  of 
any  reliable  opinion.  But  as  to  the  lines  of  the  question  I  am  fully 
convinced,  and  I  content  myself  rather  with  suggesting  those  lines 
than  with  the  expression  of  any  very  definite  opinion  thereon.  So 
serious  is  this  problem,  not  only  to  our  industry,  but  to  commerce 
itself,  that  I  am  sure  every  one  who  has  the  welfare  of  the  empire  at 
heart  will  feel  that,  whatever  one's  limitations,  one  is  quite  justified  in 
raising  one's  humble  voice  to  swell  the  chorus  now  being  raised  that 
serious,  studious,  and  practical  application  may  be  given  to  the  issue 
before  us. 

There  can  be  little  doubt  that,  till  quite  recently,  British  capitalists 
and  manufacturers  have  dozed.  The  commercial  habits  of  their  early 
days  have  been  allowed  to  be  the  only  habits  that  could  attach  to 
business  life.  Precedent  has  been  followed  instead  of  new  precedents 
being  established.  Indeed,  I  suggest  that  precedent  should  be,  com- 
paratively speaking,  a  dead  word,  for  a  new  precedent  is  scarcely 
established  before  the  environment  of  commercial  life  renders  it 
antiquated.  A  perpetual  study  should  be  given  to  the  ever-changing 
conditions  of  commerce,  and  business  should  be  continuously  adjusted 
to  these  conditions.  Fortunately,  the  commercial  instincts  of  our  day 
have  responded  to  the  uneasiness,  occasioned  by  the  wonderful 
ildvanccs  of  our  commercial  rivals,  and  the  last  few  years  have  been 
spent  in  good  work  whose  fruit  will  assuredly  be  seen. 

But  it  will  be  obvious  that  the  question  "  To  what  extent  are  we 


1903.]  OF  LEEDS  LOCAL  SECTION.  569 

equipped  for  meeting  the  future  ? "  is  not  merely  a  question  of  our  day. 
It  is  one  for  all  time.  Each  generation  must  ask  itself  that  question. 
Having  asked  it  for  our  own  day,  let  us  proceed  to  examine  it.  It  seems 
to  me  the  question  must  be  examined  under  at  least  the  following  four 
heads:  (a)  Foresight,  (b)  Management,  (c)  Education,  {d)  Fiscal 
Conditions. 

Foresight. — ^I'he  consideration  of  foresight  may  be  dismissed  in  a 
few  words.  One  instance  of  the  want  of  foresight  of  our  electrical 
manufacturers  may  be  seen  in  their  neglect  to  lay  themselves  out  some 
years  ago  to  meet  the  demand  for  the  larger  units  required  for  central 
stations,  with  the  result  that  so  many  of  the  largest  sets  were  supplied 
by  foreign  firms.  It  is  always  easy  to  speak  after  events  have  passed, 
but  that  this  demand  would  arise  for  larger  units  was  so  absolutely 
certain  and  so  perfectly  obvious  to  those  who  considered  the  subject 
that  it  is  astonishing  to  me  that  manufacturers  should  have  allowed 
themselves  to  be  in  the  invidious  position  of  seeing  orders,  which 
ought  to  have  been  theirs,  going  out  of  the  country. 

In  this  connection  I  appeal  to  our  moneyed  classes  to  realise  more 
fully  the  dignity  of  commerce,  to  sink  their  money  in  ways  that,  if  they 
do  not  yield  immediate  prospects,  will  certainly  show  handsome  future 
returns.  It  is  to  these  men  we  must  look  for  assistance  in  the  opening 
up  of  new  markets.  It  is  of  them  we  demand  that  instead  of  buying 
up  landed  estates  that  yield  but  little  either  now  or  hereafter,  they  will 
invest  in  that  which  will  ultimately  provide  them  an  ever-increasing 
yield  and  the  nation  with  a  hard-working,  intelligent,  commercial 
community. 

Management. — In  considering  this  question  we  must  do  so  in  com- 
parison with  our  competitors  abroad.  In  the  electrical  industry  it  is,  I 
say,  a  serious  reflection  on  our  manufacturers  of  electrical  plant  that 
the  bulk  of  the  orders  for  the  largest  schemes  have  gone  to  foreign 
firms,  or  at  any  rate  to  firms  of  foreign  origin.  It  gives  much  food  for 
reflection  that  to-day  the  purely  English  electrical  firms,  with  perhaps 
but  one  exception,  are  not  in  a  position  to  take  one  of  these  large 
contracts  in  competition  with  the  large  American  or  Continental  firms, 
for  the  simple  reason  that  the  English  companies  are  too  small.  I  do 
not  say  that  they  could  not  execute  the  work  from  an  engineering 
point  of  view.  I  think  they  could,  and  certainly  as  well  as  (possibly 
better  than)  the  foreign  firms,  but  I  say  that  for  financial  reasons  such 
contracts  are  prohibitive  to  them  at  present,  the  risk  with  their 
comparatively  small  capital  being  too  great  unless  they  could  get  the 
contracts  at  their  own  prices,  which  must  be  liberal.  They  dare  not 
take  such  a  competitive  contract,  for  the  reason  that  it  would  mean  that 
their  works  would  be  run  almost  entirely  for  one  job,  and  in  case  of 
any  miscalculation  they  might  be  put  into  a  very  awkward  position.  It 
is  evident  that  our  manufacturers  are  now  progressing,  but  I  am  afraid 
it  must  be  admitted  that  it  is  not  so  much  due  to  their  desire  to  obtain 
the  best  results,  but  rather  to  sheer  necessity. 

With  regard  to  the  question  of  labour,  I  think  our  inanufacturers 
must,  in  their  own  interests,  and  in  the  larger  interests  of  the  nation, 
study  this  question  seriously.     I  know  that  blame  is  laid  at  the  door  of 


570  DICKINSON  :  ADDRESS  AS   CHAIRMAN  [Leeds. 

the  working  man  for  restricted  output,  and  often  do  we  hear  the  men 
criticised  in  this  respect ;  but  is  it  just  ?  Is  the  blame  all  on  one  side  ? 
I  say  emphatically,  No.  I  believe  the  cause  of  restricted  output  is  due 
to  the  system  of  payments  generally  in  vogue.  If  you  wish  to*  get  the 
greatest  output  you  must  pay  for  it.  This,  it  seems  to  me.,  can  only  be 
done  by  paying  on  a  liberal  scale  on  the  bonus  or  premium  system,  or 
some  other  system  which  will  give  an  inducement  to  exert  best 
endeavours.  If  this  practice  were  more  general  in  England  we  should 
see  more  of  the  close  attention  and  the  steady  and  consistent  applica- 
tion to  the  work  on  hand  that  is  so  marked  in  up-to-date  workshops. 
The  greater  security  the  manufacturer  can  show  for  the  future 
maintenance  of  the  higher  wage  earning  facility  this  scheme  affords, 
the  greater  will  be  the  chance  of  the  system  becoming  general,  which 
will  be  to  the  permanent  advantage  both  of  the  manufacturer  and  the 
artisan.  It  must  be  understood,  of  course,  that  in  advocating  this 
attempt  to  obtain  increased  output,  I  am  not  advocating  in  any  way 
any  lowering  of  the  standard  of  quality  of  goods  produced. 

In  addition  to  this,  the  workman  should  be  induced  by  every  means 
to  use  his  brains  to  suggest  any  new  process  or  tool  to  facilitate  greater 
output,  and  to  do  this  it  will  be  necessary  to  compensate  him  for  his 
skill  where  it  is  found  to  be  beneficial.  I  have  often  heard  it  said  that 
the  British  working  man  has  no  brains.  I  do  not  believe  it,  and  1 
^ympathise  with  what  he  has  said,  by  his  actions,  that  he  is  not 
prepared  to  give  the  manufacturers  "  something  for  nothing."  If  he 
has  brains  he  is  capable  of  being  influenced,  and  it  is  the  duty  of  the 
manufacturer  to  see  that  he  is  properly  influenced,  and  this  can  be 
most  readily  done  by  making  it  worth  his  while  to  try. 

The  last  point  I  would  mention  under  this  heading  is  that  of 
advertisement.  There  can  be  no  doubt  that  orders  have  gone  to  at 
least  one  of  our  rivals  because  of  what  I  will  term  his  arts  in  advertis- 
ing. These  are  not  confined  to  the  orthodox  announcement  in  a  trade 
journal,  nor  to  the  apparently  inspired  leaderettes  in  the  daily  press 
and  the  monthly  magazine,  but  to  his  assiduous  and  ofttimes  daring 
approach  to  possible  users  by  careful  and  attractively  penned  letters, 
and  by  the  ingenious  ways — I  was  going  to  say  bluff — of  his  represen- 
tatives. I  think  we  underdo  advertisement  as  much  as  this  particular 
rival  overdoes  it,  and  suggest  our  manufacturers  give  more  heed  to  the 
subject.  The  moral  I  wish  to  point  is  that  the  British  manufacturer 
has  hitherto  been  too  modest  in  advertising,  and  that  the  time  has 
arrived  when  the  excellence  of  his  productions  and  his  stereotyped 
form  of  trade  journal  announcement  shall  not  be  his  only  means  of 
communicating  his  existence  to  the  world.  I  suggest  he  give  some 
study  to  the  subject  of  judicious  advertisement  and  seize  every 
opportunity  of  acquainting  possible  buyers  and  the  general  public, 
through  the  medium  of  the  daily  press  as  well  as  the  trade  journals, 
with  what  he  has  done  and  is  doing. 

Education. — On  this  subject  let  me  request  you  all  to  read  anew 
Professor  Perry's  inaugural  address  of  1900.  Whilst  I  emphatically 
disagree  (not  from  any  strained  patriotism,  but  from  reading  and 
observation)   with  the    Professor's    inference    that    British    electrical 


1903.]  OF  LEEDS   LOCAL  SECTION.  571 

engineers  are  behind  those  of  America  or  the  Continent  in  skill  or 
aptitude,  the  re-perusal  of  his  brilliant  and  practical  "  straight  talk  "  is  a 
tonic  we  should  all  take  periodically.  But,  as  I  pointed  out  in  my 
letter  which  appeared  in  the  Electrical  Times  of  the  20th  December,  1900, 
if  the  British  engineers'  theory  is  faulty  and  incomplete,  the  methods 
adopted  in  our  colleges  and  institutions  must  be  faulty  and  incomplete. 
Since  then  there  has  been  a  practical  advance  in  general  commercial 
education,  but  the  curricula  followed  are  mainly  on  foreign  lines. 
I  assert  that  we  should  be  in  the  van  of  technical  educational  progress, 
not  followers  merely.  Those  in  charge  of  this  important  department 
of  our  national  activities  should  certainly  have  associated  with  them 
representatives  of  every  branch  of  engineering,  and  they  should 
formulate  a  British  curriculum.  The  value  of  constant  and  intimate 
association  between  technical  schools  and  manufacturers  cannot  be 
overrated.  The  need  for  such  co-operation  is  growing,  and,  as  the 
benefits  of  the  secondary  schools  go  to  the  manufacturers,  I  am  quite 
sure  co-operation  will  result  in  manufacturers  helping  the  schools  with 
funds  and  plant. 

Fiscal  Conditions, — The  question  of  our  fiscal  conditions  is  one  that, 
as  I  have  already  stated,  I  am  not  prepared  to  dogmatise  upon.  On 
the  one  hand,  keen  competition  and  the  necessity  for  tackling  big  jobs, 
which  leads  to  amalgamation  and  combination,  often  ends  in  trust 
abuses,  whilst,  on  the  other,  a  mote  of  necessary  protection  may  lead  to 
a  beam  of  abuse.  Yet  there  is  no  doubt  the  tariffs  of  foreign  nations 
are  becoming  vexatious  and  require  much  study. 

As  regards  our  specific  business,  I  have  been  thinking  the  matter 
over  and  have  come  to  the  conclusion  that  there  is,  in  some  measure,  a 
degree  of  excuse  for  the  holding  back  of  our  wealthier  manufacturers  and 
financiers  from  erecting  big  works  and  laying  out  extensive  plant  when 
there  is  always  the  bogey  over  their  heads  that  empires,  which  have 
protected  their  internal  trades  by  walls  of  tariffs,  have  free  access  to 
sell  over  here  their  surplus  at  less  than  cost  price,  or  undertake  big  jobs 
at  practically  cost  price,  the  which  keeps  their  plant  fully  occupied  and 
has  an  obvious  effect  on  their  trading.  The  electrical  work  of  to-day 
and  of  the  future  renders  big  works  absolutely  essential.  Our  foreign 
competitors  when  erecting  such  can  always  feel  they  definitely  com- 
mand their  home  markets  and  can  compete  on  practically  equal  terms 
in  ours.  Have  our  manufacturers  always  to  endure  this  increasing 
restriction  abroad  and  still  be  weighted  by  not  even  having  their  home 
markets  secured  ? 

I  fully  appreciate  and  most  earnestly  sympathise  with  our  British 
artisan,  and  think  everything  should  be  done  that  can  be  done  to  elevate 
and  help  him.  But  the  question  naturally  arises  :  "  Is  it  not  possible  to 
cover  the  increased  price  of  necessaries  which  might  arise  if  we  adopted 
some  measure  of  protection  by  the  extra  work  this  country  would  obtain 
and  the  higher  wages  it  might  pay,  and,  at  the  same  time,  might  not 
other  possible  grievances  be  foreseen  and  foreguarded  by  systems  of 
bonus  or  profit  sharing  ? "  It  may  be  that  the  welding  together 
of  the  British  Empire  will  largely  reduce  the  poignancy  of  the  ques- 
tion of  free  trade  as  it  stands  to-day,  but  that   is  ^  matter  of  very 


672  DICKINSON :  ADDRESS  AS  CHAIRMAN.        [Leeds,  1903. 

considerable  time,  involving  as  it  does  the  fiscal  policies  of  young 
nations. 

Under  this  head,  too,  the  question  arises  as  to  whether  our  Govern- 
ment gives  sufficient  consideration  to  trade  questions.  We  are  agreed 
that  we  do  not  want  too  much  Government  interference.  But  I  am 
heartily  in  accord  with  the  movement  now  being  mooted  by  eight 
Chambers  of  Commerce  that  the  time  has  arrived  when  we  should  have 
a  Minister  of  Commerce,  whose  duties  should  be  initiative  rather  than 
administrative,  whose  time  should  be  absorbed  in  Ending  openings  for 
trade  and  advising  on  all  matters  concerning  the  conditions  of  trade 
abroad.  In  this  direction  invaluable  work  is  being  done  by  the  Com- 
mercial Intelligence  Department  of  the  Board  of  Trade.  But,  good  as 
is  the  work  of  this  department,  it  only  goes  to  prove  the  necessity  of 
its  having  a  separate  existence.  The  administrative  work  of  the  Board 
of  Trade  is  vast.  What  we  need  is  some  one  who  is  free  to  initiate  antf 
who  will  be  responsible  for  any  neglect  in  this  direction. 

I  hope  r  have  made  it  quite  clear  that  I  advance  neither  the 
doctrine  of  free  trade  nor  that  of  protection.  What  I  do  assert  is  that 
the  question  is  a  grave  one,  immediately  demanding  further  study,  and 
I  plead  that  pressure  be  brought  to  bear  on  those  in  high  places  at  once 
to  collect  and  study  the  data  necessary  for  arriving  at  a  conclusion 
to  lay  before  the  nation. 

In  conclusion,  let  me  assure  you  I  am  no  pessimist.  If  we  have 
not  kept  abreast  of  the  times  it  has  been  for  reasons  that  would  perhaps 
largely  have  led  to  others  becoming  lax  had  they  been  in  our  place. 
The  British  manufacturer  is  a  man  with  a  level  head  and  a  lion's  pluck, 
and  he  has  awakened  from  his  slumbers.  The  British  workman  is  a 
good  fellow.  I  tell  you  I  have  been  all  over  the  British  Isles  on  the 
one  hand,  and  on  the  other  hand  I  have  visited  many  big  works  in  the 
principal  towns  of  the  United  States,  Germany,  Austria,  and  elsewhere, 
and,  whilst  allowing  for  the  disadvantages  of  flying  visits,  I  did  not  go 
with  my  eyes  shut,  and  I  tell  you  that  for  solid  good  work  we  are 
unrivalled.  To  this  good  property  we  are  soon  to  add  the  advantages 
of  our  new  interest  in  Technical  Education  and  the  like,  and  if  only 
employers  will  devote  themselves  to  the  earnest,  strenuous  study  of 
inter-trade  problems  and  can  see  their  way  to  bring  men  to  be  paid  on 
results — and  in  no  mean  spirit — the  prospects  of  the  old  country  in  the 
future  are  as  great  as  ever  they  have  been  in  the  past. 


THORNTON:    SYNCHRONOUS  CONVERTERS. 


673 


NEWCASTLE  LOCAL  SECTION. 


EXPERIMENTS  ON  SYNCHRONOUS  CONVERTERS.  \^ 
By  W.  M.  Thornton,  D.Sc,  Member. 

(Paper  read  at  Meeting  of  Section^  December  /,  igo2.) 

§  I.  The  growth  of  large  schemes  for  the  electrical  transmission  of 
energy  by  high-tension  alternating  currents  is  probably  the  most 
remarkable  feature  in  modem  industrial  development.  The  success  of 
these  schemes  depends  mainly  on  unfailing  regularity  of  supply,  and 
this  again  on  the  stability  of  the  electromagnetic  system  of  generators, 
line,  and  motors  under  all  loads.  Those  responsible  for  these  schemes 
make  very  cautious  experiments,  the  cost  of  misadventure  is  too  great, 
and  the  machines  themselves  are  rarely  available  under  all  the  conditions 
necessary  for  a  complete  study  of  their  behaviour.  I  had  the  pleasure 
of  making  some  observations  of  wave-forms  on  the  synchronous  motor 
system  of  the  Wallsend  scheme,  and  these  suggested  that  a  more 
detailed  research  into  the  working  of  the  two  synchronous  converters  * 
in  the  college  laboratory  might  add  to  our  knowledge  of  the  complex 
reactions  within  the  armature  of  this  and  aUied  classes  of  machinery. 
The  research  is  entirely  experimental.  There  are  so  many  variables 
that  it  is  useless  to  attempt  to  construct  a  theory  including  all  of  them. 
Steinmetz  and  S.  P.  Thompson  have  given  analyses  of  the  ideal  case 
in  which  the  magnetism  is  distributed  sinusoidally  around  the  circum- 
ference of  the  armature.  But  though,  as  will  be  seen,  the  generated 
voltage  wave-form  at  no  load  closely  approximates  to  a  sine  curve,  this 
can  only  be  obtained  by  a  magnetic  distribution  which  is  not  sinusoidal. 
Kapp  has  considered  the  variation  of  output  with  relative  breadth  of 
pole,  showing  that  within  practical  limits  the  output  is  less  for  the  same 
armature  heating  when  the  poles  are  broader.  In  Table  I.,  I  quote  his 
figures  for  two  cases,  and  have  calculated  corresponding  values  for  the 
machines  used  in  these  experiments,  which  are  not  specially-designed 


Table  I. 

Type 

1 

Phase  dis- 
placement. 

Sine 
distribuUon. 

Pole  breadth  -r  pole  pitch. 

§ 

h 

•61 

•88 

Single-   ( 

phase    J 

conver-  j 

ter      ( 

COS0=   I 

=  7 

85 
6o 

88 
81 
73 
63 

11 

80 
70 

83-6 

70-5 
62-3 

541 

¥^ 
67         , 

57*2    ^ 

Three- 

COS^  =  *I 

134 

138 

144 

160 

160 

phase 
converter 

=    Q 

=  •8 

J    not  cal- 
)    culated. 

128 
117 

137 
126 

149 
132 

146 
132 

574 


THORNTON  :    EXPERIMENTS   OX 


[Newcastle, 


converters.    The  figures  are  percentages  referred  to  the  same  machine 
working  as  a  direct-current  generator  for  equal  armature  heating  in  each 
case.    In  the  last  two  columns  are  the  values  which  might  be  expected 
from  the  two  machines  used  calculated  in  the  same  way  as  Kapp's. 
The  alternating  current,  i,  which  heats  the  armature  to  the  same  degree 

as  the  direct,  i„  is  i=  — ^-/„^'  the  values  of  q  being  given  in  Table  VII., 
and  from  this  relation  the  latter  part  of  Table  I.  was  obtained.     The 


results  are  not  total  efficiencies.  The  w.itts  lost  in  the  field,  friction, 
windage,  and  eddy  currents  are  all  omitted,  but  the  results  are  instruc- 
tive, as  showing  the  variations  in  the  principal  source  of  loss  of  efficiency. 
The  comparative  values  of  Table  I.  are  plotted  in  Fig.  i.  Most  of  the 
curves  show  that  the  relation  between  power  factor  and  efficiency  is 
not  linear,  the  curvature  being  generally  upwards.  The  Scott  and 
Mountain  single-phase  curve  is,  however,  the  reverse  of  this,  and  in 
both  single  and  three-phase  sets  the  armature  heating  is  approximately 
•  K.ipp,  Dynamos,  Alternators,  and  Transformers,  p.  476. 


1902.] 


SYNCHRONOUS   CONVERTERS. 


675 


in  inverse  proportion  to  the  power  factor.  The  meaning  of  the  curves 
drooping  towards  the  low  power  factor  end  is  in  these  cases  the  loss  of 
efficiency  due  to  change  of  distribution  of  the  current  in  the  armature, 
and  has  nothing  to  do  with  the  effect  of  the  eddy  currents  in  the  poles. 
§  2.  The  object  of  the  experiments  was  to  find  how  the  efficiency  of 
the  plant  varied  with  load  for  all  conditions  of  excitation,  to  find  any 


J, 
< 


l!=R^ 


i. 


fP 

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«-!  . 

^  iS  c 
^  fe'£ 

.-  o  C/3 

ta^  - 
s  *  c 

c  O  g 

C    w  C/3" 

'^  .£  'I 

^:5  rt  £ 


C/3    «  < 

o  fcu  a  J- 

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>  iS  w   o 

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S  J3  -c  i 


I  0^  k:^ 
<^  a  J  t: 


discrepancies  between  the  theoretical  and  observed  losses,  and  to  locate 
the  causes  which  would  give  rise  to  them.  At  the  same  time,  it  was 
thought  that  records  of  the  changes  of  wave  shape  might  throw  some 
light  on  the  nature  and  magnitude  of  the  armature  reactions.  The 
greatest  difficulty  in   synchronous  converter   working  being  periodic 


676 


THORNTON:   EXPERIMENTS  ON 


[Newcastle, 


lb 
% 


S 


3 
lb 


C 

o 


a 

3 


19Q2.] 


SYNCHRONOUS   CONVERTERS. 


677 


I 

c 


c 
>> 

CO 


o 
•J 

c 


(x3 


£ 


to 

c 

o 


fluctuations  started  from  irregular  turning  moments  in  the  prime 
mover,  the  first  machine  was  driven  throughout  from  a  set  of  storage 
cells.  Fifty-two  of  these  were  used  to  drive  a  9-kw.  bipolar  machine 
(Scott  and  Mountain),  the  armature  of  this  being  ring- wound  and  pro- 
vided with  slip-rings,  so  that  single,  two,  or  three-phase  current  could 
be  taken  and  supplied  to  a  5-kw.  machine  (Holmes),  also  bipolar  and 
ring-wound  in  the  same  way.  From  the  second  converter  direct 
current  was  led  through  an  adjustable  liquid  resistance.  The  field  of 
each  machine  was  separately  excited  from  the  same  cells.    A  direct- 


678 


THORNTON:    EXPERIMENTS   ON 


[Newcastle, 


reading  Siemens  and  Halske  wattmeter  was  inserted  in  the  line  in  series 
with  a  standard  low  resistance,  from  the  terminals  of  which  connections 
were  made  to  one  strip  of  a  double  oscillograph.  The  other  strip  was 
placed  in  series  with  a  non-inductive  resistance  across  the  line  terminals 
in  turn.  The  resistance  and  capacity  of  the  cables  connecting  the 
machines  were  always  negligible.  The  general  arrangement  of  the 
connections  is  shown  in  Fig.  2.  There  is,  it  will  be  seen,  a  double  con- 
version of  current,  and  one  point  of  interest  brought  out  by  the  experi- 
ment was  that  the  heating  losses  of  the  system  could,  by  varying  the 
excitations,  be  moved   from  one  machine    to  the  other.      The   two 


ttU>f(f!M. 


Fig.  3. 


machines  were  run  up  together  from  rest  coupled  by  the  cables  alone, 
and  the  load  gradually  thrown  on.  Throwing  it  on  suddenly  started 
violent  phase  swinging  in  the  second  converter,  which  measured  in  one 
case  50  deg.  difference  between  the  limits  of  the  current  wave  positions,  as 
shown  by  Curve  22,  Plate  11.-='  The  highest  frequency  possible  was  23 
alternations  a  second.  The  first  set  of  experiments  was  made  to  find 
the  relation  between  total  plant  efficiency  and  power  factor.      The 

•  Greater  swings  might  have  been  observed,  but  whenever  the  amplitude 
increased  beyond  the  above  limit,  the  oscillograph  synchronous  motor  came 
out  of  step. 


1902.] 


SYNCHRONOUS   CONVERTERS. 


579 


obscr\'ations  are  given  in  the  following  tables,  and  the  magnetisation 
curves  of  the  machines  in  Fig.  3.  From  the  latter  an  estimate  of  the 
saturation  of  the  magnetic  circuit  may  be  formed.  The  reluctance  of 
the  Scott  and  Mountain  at  full  excitation  is  '004SS,  and  of  the  Hohnes 
'OOS2y,  and  the  lengths  of  the  air-gaps  are  riscm,  and  I'oOcm. 
respectively. 

A. 

265 


331     26. 
32 


I 


•85 


75 


.31 

i  29 
[28 
'  27 

2<^' 

34! 
23 1 


255 


245 


235 


■^ 

"N, 

\ 

// 

^ 

^ 

y 

X 

\ 

\ 

/ 

i 

^ 

\ 

/ 

\ 

\ 

/ 

{ 

V 

-^ 

X 

\ 

1*4  1-6  18  20 

Exciting  Ctsrrmf.    S.  &  M. 

Fig.  4. 


2-4 


Table  II.  (Fig.  4). 

Field  of  first  converter  varied.    Motor  field  constant.     Loss  in  motor 
field,  330  watts.     Motor  output  kept  as  nearly  as  possible  constant. 


First  converter  input. 


Volts 


70 

71 
72 

74 

75 
75'2 

74*5 

76 

76 


28-5 

27*5 
263 

25 

24 

235 

24 

23 

22*5 


F.  C. 

Speed. 

i-.s.s 

i,coo 

1*62 

1,000 

170 

9QO 

i«5 

980 

1-98 

950 

2'IO 

930 

212 

900 

2*34 

920 

2-55 

930 

37 
37 
37 
37 
37 
37 
37 
37 
37 


Motor  input. 


455 :  323 

465  I  30 

47*0  I  28-2 

48-0  j  25-3 


482 
48-5 
47-8 
48-1 
480 


241 

240 

25-25 

259 
29-3 


Motor  out- 

Effi- 

put. 

ciency 
Z 

W.       Cos0 

V. 

A. 

1,125  ;  -85 

72 

8-2 

246 

1,250    90 

72-4 

p 

253 

1,225  '  '93    72-4 

8-3 

25« 

I1I74     97    72*4 

8-2 

260 

1,165    '99    72 

8-1 

26-1 

1,134.   97  1  70*6    8-2 

26-1 

1,150     95    70     1  8-0 

25-6 

1,100    -89 

69     1  8-0 

247 

1,074    76 

67     1  7-8 

235 

It  will  be  seen  that  the  maximum  efficiency  is  reached  a  little  before 
the  minimum  current. 


580 


THORNTON:    EXPERIMENTS  ON 


[Newcastle 


•95 


r 


•85 


75 


235 
23 

2a-5 
22 
^21-5 

•S  21 

t«J  205 
20 
19-5 
19 

18-5 

18 

17-5 


B. 


34 


^30 


Q   28 


26 


••■■I*  Y /  / ■  


1*5 


2  2-5 

Exciting  Current.    Holmes. 


3'5 


Fig.  5. 


Table  III.  (Fig.  5). 

Field  of  first  converter  constant.  Motor  field  varied.  Loss  in  first 
converter  field,  116  watts.  With  the  same  input  as  in  Table  I., 
the  output  and  efficiency  are  less. 


First  couv 

srter  input. 

Motor  input. 

Motor  out- 
put. 

Effi- 
cienc>'. 

Volts. 

A. 

F.C. 

Speed. 

F.  C.        V. 

A. 

w. 

Cos0 

V. 

1 

A.    1      % 

,  73 

261 

2 

1 

980    37 

48-2 

258 

1,210 

•97 

72 

7*4 

1 
22*6 

74 

25-8 

2 

990    3-29 

485 

24-5 

1,180 

•99 

71-6 

7*4 

23-2 

74*1 

25*4 

2 

1,100    2-98 

48-5 

24 

1,150 

•99 

706 

7*3 

23*6 

74-2 

25-2 

2 

1,010  1  27 

^5 

23-5 

1,129 

i*o 

T. 

7*1 

229 

75 

25 

2 

1,030  1  2-5 

^^0 

237 

1,104 

•97 

70 

23-5 

75*1 

244 

2 

1,040  j  2-3 

47-8 

24-5 

1,079 

? 

^K 

7-0 

225 

75*1 

24-4 

2 

1,060   2-17 

47*2 

253 

1,069 

65-8 

6-9 

21*9 

75-3 

24-2 

2 

1,070   2*03 

47 

^7, 

1,060 

'S3 

64 

6-7 

210 

75-« 

24-1 

2 

1,080    1*93 

46-9 

27-8 

1,044 

•8 

63 

6-6 

20'5 

75-« 

24-1 

2 

1,090 

1-83 

46-2 

29 

1,034 

77 

62 

6-3 

19-2 

75-« 

24-1 

2 

1,090 

175 

46 

30-I 

1,024 

74 

6o-8 

61 

i8-4 

75-» 

242 

2 

1,100 

1-67 

45*5 

31-1 

1,019 

74 

59-8 

60 

178 

1902.] 


SYNCHRONOUS  CONVERTERS. 


581 


■95 


^     -9 


•75 


32 


if 

2  28  t*! 


a8% 


627% 


26 


26% 


25% 


-=3=-^ 

\ 

X 

"^ 

-^^0^^ 

\ 

// 

\ 

y 

/ 

\ 

// 

\^ 

7 

/ 

15 


2*0  25 

Exciting  Current.    Holmes. 

Fig.  6. 


30 


35 


Table  IV.  (Fig.  6).     ^ 

Field  of  first  converter  constant.    Motor  field  varied, 
motor  kept  constant. 


Current  from 


Finsl  converter  input.                                 Motor  input. 

Motor  out- 
put. 

Effi- 
ciency. 

V. 
71-4 

A. 
27-6 

F.  C. 

Speed. 

F.  C.  1     V. 

1 

A. 

28 

W. 

Cos0 
•96 

V. 



A. 
91 

% 
26*4 

2 

940 

3-6 

46*2 

i»255 

71-4 

27 

2 

950    3*2 

464  1  27 

1,234 
1,189 

•98 

69 

91 

274 

73 

26 

2 

990    2-66 

468  I  256 

•99 

672 

9-1 

28*0 

73*2 

25« 

2 

1,000    2-28 

46     ,  262 

1,160 

•97 

647 

9-1 

27*6 

74 

25-8 

2 

1,030 

2-0 

45*2  ;  27-9 

1,139 

•90 

61-5 

9-1 

264 

25-8 

74 

25-6 

2 

1,040 

vH 

44-8  1  30-0 

1,109 

•82 

594 

91 

74 

25-9 

2 

1,060 

1-65 

43'8    32-1 

1,0891  77 

1 

57 

91 

24*9 

582 


THORNTON:    EXPERIMENTS   ON 


[Newcastle, 


The  conclusion  to  be  drawn  from  the  above  figures  is  that,  as  one 
would  expect,  the  efficiency  is  greatest  when  the  power  factor  is  unity, 
whichever  field  is  varied^  and  it  is  of  interest  to  note  the  close  relation 
between  power  factor  and  efficiency  over  a  wide  range  of  excitation 
while  the  output  is  maintained  constant.     Plotting  the  square  of  the 


I' 

9rK 

\ 

1 

So, 

"^. 

■^^ 

K. 

7^ 

^"v. 

ef^/cii 

NCY 

25 

u 

'                     5/ 

Fig.  7. 

continuous  armature  current  against  efficiency  (Fig.  7),  it  is  found  that, 
except  at  low  magnetisations,  they  are  proportional.  At  low  excitations 
the  effect  of  the  large  idle-current  component  is  evident.  In  order  to 
see  whether  the  higher  efficiency  was  maintained  at  all  loads  when  the 
excitation  was  adjusted  for  the  minimum  armature  current  found  above, 


Fig.  8. 


1902.] 


SYNCHRONOUS  CONVERTERS. 


sas 


three  more  sets  of  readings  were  taken,  shown  in  Fig.  8.  The  second 
converter  fields  were  kept  constant  in  each  test  while  the  load  was 
varied.  The  improvement  in  efficiency  obtained  at  light  loads  is  seen 
to  be  maintained  at  the  higher. 

§  3.  The  next  experiment  was  a  variation  of  the  last,  the  machines 
being  run  under  all  conditions  of  excitation,  and  readings  being  taken 
of  all  the  variables,  including  the  wave-forms  of  the  line  current  and 
voltage.  The  results  with  the  calculated  efficiencies  are  in  Tables  V. 
and  VI.,  and  Figs.  9  and  10  are  plotted  from  these.  The  number  of  the 
curves  refers  to  Plate  II.  The  remarkable  'feature  of  the  curves  is 
their  sudden  droop  at  loads  which,  compared  with  the  ordinary  con- 


50% 


45% 


40% 


§35% 


I 


30% 


25% 


ao% 


^ 

\ 

// 

/• 

:i 

/> 

/ 

1 

fi 
1 

— —  ui 

«?MAL  EX 
fER 
DER 

CITATION 

•• 

/ 

1,000 

WatU  Output. 


3.000 


Fig.  9.— Single-Phase  Converters. 

tinuous-current  output,  are  small.  The  reason  for  this  appears  more 
clearly  when  the  machines  are  worked  from  the  main  generator,  wliich 
being  driven  by  a  single-cylinder  engme  has  an  irregular  turning  moment. 
It  was  almost  impossible  to  reach  high  loads  without  the  second  con- 
verter coming  out  of  step,  and  the  only  way  to  obtain  them  was  to 
over-excite  the  second  machine  and  so  reduce  the  eddy-current  losses 
and  magnetic-current  fluctuations  and  gradually  lower  the  excitation 
as  the  load  was  increased ;  even  then  the  machine  soon  worked  up 
a  phase  swing  and  came  put  of  step.  Fortunately,  both  armatures 
have  considerable  inductance,  about  -002  henry,  between  the  slip- 
rings,  single-phase,  and  there  were  no  Ul  effects  beyond  the  racing 
of  the  first  machine.  This  was  the  first  intimation,  as  a  rule,  that  the 
second  had  broken  step,  and  it  was  always  necessary  to  keep  some  one 
by  the  main  switch  of  the  first  machine  to  break  the  current  before 
the  armature  had  accelerated  to  destruction.  The  advantage  of  normal 
excitation  is  most  marked  at  the  higher  loads  in  both  Figs.  9  and  i  J. 
Vol.  82.  89 


584 


THORNTON:   EXPERIMENTS  ON 


[Newcastle, 


Table  V.  (Fig.  9). 

Single-Phase  Converters,     Variation  of  Load  with  excitation  constant. 

Field  Currents  :  First  Machine,  2  Amperes ;  Second,  i'93. 

(Second,  Under-excited.) 


i 


9 
10 


First  Converter 
input. 


Ac 


73  I  31 

722  40 

755 !  505 

71  I  62 

80  I  71 

I 

692  40 


II  I  77  !  81 


w 


2260 
2890 
4^50 
4400 
5680 
2768 
6240 


Second  Converter  input. 


Second  Converter 
output. 


Arm.iturc 
Efticiencics  X 


464 

442 

1400 

464 

51 

1976 

43-6 

.63 

2640 

40 

74 

2948 

45 

845 

3768 

42 

482 

1864 

412 

96 

3944 

Coe0 

V. 

Ac 

•68 

53 

13-4 

•83 

52 

227 

•96 

55 

322 

•99 

50 

39 

•99 

56 

44 

•92 

54 

22-5 

10 

52 

50 

W      istc.  2nd  c.  Total., 


710      62   1507    287 


1 1 80    687 
1780    695 

1950      67 

I 

2494  66-5 
i2i5|67-4 

2600    63 -2 


59«  ,  383 
67-5,   44 

66    42*2 

I 

657  1 420 

65  410 

66  140-5 


Field  Currents  :  First  Machine,  2  Amperes  ;  Second,  272. 
(Second,  Normal.) 


12 

73 

36 

2630  466 

40 

1840 

i*o 

68 

1875 

1275 

74 

49 

3620  46 

57 

2620 

ro 

67 

2875 

1925 

13 

805 

61 

4900 

496 

70 

3464 

10 

72 

355 

2550 

14 

725 

100 

7250 

36 

120 

4348 

ro 

52 

465 

2880 

70  1 693 '437 


71-2, 73*5 
707  1 73*6 


49 
49 


60  1 664     38 


Field  Current   :  First  Machine,  2  Amperes  ;  Second,  3-29. 
(Second,  Over-excited.) 


15 

16 
17 

18 


71 
75 
78 
75 

56 
50 


40 
49 
72 
80 


2840 1  46 
3660 [  47 
5616  \  465 
6000 1  432 


44  1 2000 :  ro  i  687  ;  1875   1275 


56  2636 
84  1 3856 
95  14008 


1*0     705  257  1820 

•99     70  ,  365  '  2560 

I         I  i 

•98     65  I  385  ^ 2500 


702  16375  395  J 

717 1   69  ,   45  I 

685  695  1 42-5  j 

68    613' 395  i 


Field  Currents  :   First  Machine,  16  Amperes  ;  Second,  27. 
(First,  Under-excited.) 


40 
44 


2240  44  1  45 

1500 

76 

561  157 

885 

2200  32  i  50 

1500 

•94 

505  17' I 

865 

67  ;   59    360 
68-2  1 57*6 '  360 


Field  Currents  :  First  Machine,  3-1  Amperes  ;  Second,  27. 
(First,  Over-excited.) 


19    63-5     33    2260 


20 
21 


76    455 
71    575 


3460 
4080 


77      72    5540 


42 
46 

405 
43 


47     1480 1    75   566    15-5    .    875  655  J  597  I  32-5 

57  2400 ;  92  61  275  1 1675  695 i  70  ! 428 


70  2860 1  ro  152-2 
88  '3880'  1-0  '  55 


I 
385  j  2010  70  I  68  1 445 

50  1 2750 '  70  ,  71  460 


1902.] 


SYNCHRONOUS  CONVERTERS. 


585 


is 

^^^ 

— 

^'"^ 

-*.^ 

^ 

/  / 

A 

SS             i 

// 

/ 

/ 

/ 

/ 
/ 

So 

1 
1 
1 

wAm 

ourm/r 

Fig.  10.— Three-Phase  Converters. 

Table  VI.  (Fig.  xo). — Three-Phase  Converfers. 

Field  Currents  :  First  Converter,  i'9  Amperes  ;  Second,  3*62. 
(Second,  Over-excited.) 


>        First  Converter 
a    1             input. 

0    ' 

Second  Converter  input. 

^•|v. 

Ac 
36 

w 

Va 

A. 

W      Co«0 

23      75 

2700 

44 

23 

1794 

•75 

,    79 

44 

3470 

45*2 

33 

2480 

•74 

24      «5 

.54*5 

4630 

50 

39 

3352 

•75 

25    81*5 

69 

5620 

46 

53 

4122 

•75 

26      77 

82-5 

6350 

406 

66 

4650 

•75 

Second  Converter 
output 


Armature 
Efficiencies. 


30 
31 

32 


76 

78 
84 

77 
71 


Ac 


198 
27 

3475 

475 

58-5 


w 


1500 
2106 
2920 
3660 
4160 


.stc. 

jndc. 

Tolal. 

66-5 

83-6 

55 

714 

«s 

60-5 

72-5 

»7-2 

63 

753 

887 

<)5 

735 

89-5 

65-5 

Field  Currents  :  First  Converter,  1-9  Amperes  ;  Second,  2*4. 
(Second,  Slightly  Under-excited.) 


27 

75 

37*5 

2815 1  43*2 

27 

2472 

ro 

74 

20 

1480 

88 

60 

.  70 

46 

32201   39 

353 

2480 

•98 

66 

28 

1848     77;  74*5 

28 

755 

435 

4050     42 

40 

2950 

•96 

71 

35 

2485 

727 

842 

70 

67 

4690  37*5 

,52*5 

3175 

•94 

62 

47 

2914 

677 

92 

29 

78 

8( 

6320     65 

05 

4210 

•91 

69 

58-5 

4030 

667 

96 

52*5 
57 
60 

63 
637 


Field  Currents  :  First  Converter,  i  '9  Amperes  ;  Second,  i  '95. 
(Second,  Under-exdted.) 


68      39 


655 
69 

64 


525 

66-5 

81 


2650 
3440 
4580 

5174 


37*5  33  12600 1 10 
365  43  ,3200,10 
545  4160!  10 


361 
33 


67  4370  96 


635 

21-3 

1350 

98 

52 

50*9 

58 

34 

1972 

93    617 

57*3 

6i 

47 

2870 

91 

69 

62-6 

52 

595 

3090 

85 

707 

597 

686 


THORNTON:    EXPERIMENTS  ON 


[Newcastle, 


§  4.  To  illustrate  the  difference  between  theoretical  and  actual  losses 
Table  VIII.  was  prepared.  The  heating  was  calculated  by  the  formula 
Pu=sq  rCj  q  having  the  following  values,  and  r  being  the  resistance 
per  radian  of  armature  circumference  : — 

Table  VII. 
Values  of  q. 


- 

First  Converter. 

Second  Converter. 

Single-phase. 

Three-phase. 
174 

Single-phase. 

Three-phase. 

*  = 

1-285 

1-375 

17s 

COS  ^  =    I 

=  7 

14-11 
1982 
25-27 
3352 

3-85 

4*37 
5-6i 

ir99 

i8-55 

22 
30 

4-62 

■     S-6i 

Table  VIII. 
Watts  Lost  in  Armature. 


Single-phase 

First  Converter. 

Second  Converter. 

CaL 

Obs. 
860 

CaL 

Obs. 

915 

225 

955 

914 

435 

796 

1,121 

1,510 

650 

760 

1,585 

M50 

876 

998 

2,120 

1,910 

1,150 

i.*94 

745 

904 
2,296 

348 

649 

2,720 

1,440 

1.344 

531 

790 

205 

565 

995 

1,000 

475 

695 

1,520 

1,536 

725 

914 

4,100 

2,902 

1,260 

1,468 

655 

820 

200 

72s 
816 

982 

1,044 

s 

2,175 

1,760 

1,290 

2,715 

1,992 

890 

1,508 

1,160 

740 

255 

6t5 

891 

700 

304 

635 

805 

780 

250 

60s 

1,000 

1,060 

850 

725 
850 

1,350 

1,220 

2,120 

1,660 

1,440 

1,130 

Three-phase. 


First  Converter. 
Cal. 


318 

475 

727 

1,165 

1,685 

190 

297 

272 

620 

1,015 

212 
380 
614 

913 


Obs. 


906 
996 

1,278 

M98 
1,700 

343 

740 

1,100 

1,515 
2,100 

50 
240 
420 
840 


Second  Converter. 


Cal. 


Obs. 


107 

294 

202 

374 

333 

432 

625 

462 

952 

490 

69 

992 

140 

632 

226 

565 

^ 

261 
180 

78 

1,250 

200 

1,228 

378 

1,290 
1,280 

607 

Values  of  r,  ohms  per  radian. 
First  Converter,  '036  (S.  and  M.). 
Second  Converter,  '0446  (Holmes). 


1902.]  SYNCHRONOUS  CONVERTERS. 


587 


Fig.  II.— Second  Under-excited. 

fyoao 

1 

1 

3^00 

j 

1 

i 

1 

1 

\ 

1 

1 

i 

1 

i 

1 

!  ^ 

^/lOO 

1 

if 

if 

jSoa 

1/ 

// 

y 

//)ao 

&» 

S.M, 

^      h»775  (?i/r/vr 

^ ' 

Sooo 


Fig.  12. — Second  with  Normal  Excitation. 


588 


THORNTON  :    EXPERIMENTS   ON 


[Newcastle, 


The  general  differences  between  observed  and  calculated  losses 
may  be  better  seen  from  Figs,  ii  to  17,  drawn  Table  VIII.,  the  former 
being  shown  by  full  lines,  the  latter  by  dotted.  In  all  the  curves  the 
ordinates  are  armature  loss  in  watts,  the  abscissae  output  of  each 
machine.  In  the  single-phase  tests  the  first  converter  losses  were  in 
most  cases  in  excess  of  those  in  the  second,  but  the  difference  between 
observed  and  calculated  loss  was  greater  in  the  second  than  in  the  first. 
The  three-phase  curves  are  more  remarkable.  In  Fig.  15,  which  refers 
to  over-excitation  of  the  second  machine,  the  differences  are  much  less 
in  this  than  in  the  first.  Fig.  16  at  nearly  normal  excitation  shows 
a  reversal,  which  is  more  strongly  marked  in  Fig.  17,  where  the  second 
converter  field  is  very  weak.  The  inevitable  conclusion  from  this  last 
set  is  that  the  armature  reaction  harmonic  is  of  sufficient  strength  to 


Fig.  13. — Second  Over-excited. 


disturb  the  whole  circuit,  so  that  the  magnetism  is  rapidly  weakened 
and  strengthened  in  the  solid  magnet  frame  sufficiently  to  cause  con- 
siderable loss  of  energy,  and  that  a  change  of  excitation  in  the  one 
machine  can  cause  a  disproportionate  change  in  the  losses  of  the  other, 
unless  by  skilful  design  and  the  use  of  damping  coils  these  fluctuations 
in  the  magnetic  circuit  are  minimised.  In  comparing  these  machines 
with  motor-generators,  it  should  be  remembered  that  there  are  similar 
disturbances  in  synchronous  motors.  Beats  can  always  be  heard,  and 
each  of  these  means  a  loss  of  energy  by  eddy  currents  in  the  iron  of 
the  magnetic  circuit.    In  F^ig.  18,  I  have  drawn  from  Tables  V.  and  VI. 

•  Vide  Kapp.  loc.  cit.  p.  475. 


1902.] 


SYNCHRONOUS   CONVERTERS. 


589 


the  separate  efficiencies  of  the  machines  for  three-phase  working,  in 
which  again  there  is  a  remarkable  effect.  The  efficiency  of  the  first 
converter  when  the  second  is  under-excited  falls  instead  of  rising  with 
tlie  load,  as  much  as  i8  per  cent,  in  one  case,  its  own  field  being  main- 
tained constant.    This  again  points  to  an  abnormal    increase  in  the 


]^a» 


Fig  14. — First  Over-excited. 


2m« 

4<M1 

^ 

-7SM. 

hoc 
Sit* 

.^' 

• 
/ 

^^^^ 

■ —          y 

.^  H. 

6 

rr 

""^Z^ 

►v^fia 

o*jrm/r 

Zooo  3ooo 

Fig.  15. — Over-excited. 


Uooo 


eddy-current  losses.  There  is  also  a  curious  drop  in  curve  I3,  which 
indicates  that  the  sudden  loss  of  total  efficiency  shown  in  Fig.  10  for 
under  excitation  takes  place  in  the  first  converter.  It  remains,  then,  to 
prove  experimentally  that  these  losses  are  caused  by  armature  reaction, 
and  to  estimate  their  magnitude. 


590 


THORNTON  :    EXPERIMENTS   ON 


[Newcastle, 


§  5.  I  have  worked  out  in  a  former  paper  *  a  numerical  example  of 
the  losses  due  to  eddy  currents  in  magnet  cores.  These  can  be  cal- 
culated when  the  dimensions  and  conductivity  of  the  core  and  the 
ampere-turns  producing  the  change  are  known.  Thus  if  c  be  the 
radius  of  the  core,  /  its  length,  ft  the  permeability,  p  the  specific  resist- 
ance, /  the  frequency  of  alternation  of  magnetism,  and  (IT)  the 


ISoa 


Zoa 


/Sbo 


/06C 


Sbc 


A>oo 


Zooo  Sooo  fooo 

Fig.  i6.~Slightly  Under-excited. 


^000 


Jk\. 

/OOC 

SCO 

A 

f 

.M. 

0 

,^--^" 

-- 

^ 

.*»-'^*'' 

MM77S 

ourmn. 

1000 


Zcoo  Jooo    "  J^o 

Fig.  17. — Under-excited. 


maximum  value  of  the  ampere-turns  causing  the  change — this  being 
sinusoidal — then  to  a  first  approximation,  the  watts  lost  f 

P 

•  •'Rotary  Converters  and  Phase  Swinging."     The  Electrician^  Sept.  27 
and  Oct.  4,  1901. 

t  Heaviside,  Electrical  Papers^  vol,  i.  p.  353. 


1902.] 


SYNCHRONOUS  CONVERTERS. 


691 


To  apply  this  to  explain  the  difference  between  the  observed  and 
calculated  losses  it  is  first  necessary  to  know  the  ampere-turns  of 
armature  reaction  for  any  given  condition  of  working.  This  was  first 
done  in  these  experiments  by  placing  a  hot-wire  galvanometer  across 
the  otherwise  unused  series  windings  of  the  Holmes  machine,  these 
forming  an  exploring  coil  of  58  turns.  About  one  volt  was  observed 
when  running  light,  and  photographs  were  taken  showing  the  influence 
of  phase  swinging  on  the  magnetic  circuit  when  unprovided  with 
damping  coils.    It  occurred  to  me  later  that  this  voltage  is  sufiicient 


\ 

\, 

y" 

Sx 

V 

"^ 

/ 

• 

m 

V  ^ 

-^ 

A 

Vi*. 

-TL. 

u 

\ 

\ 

\ 

/ 

1' 

> 

nT 

—It 

^1I». 

/ 

/^ 

"^ 

.X*. 

k 

'   / 

/ 

Si 

/ 

JL^  9umHrcf  uMomm  otarmo. 

« 

/ 

00 

TPUTorSteONO  CONVERTER . 

Fig.  18.— Variation  of  Efficiencies — Three-Phase. 


to  give  good  readings  using  the  oscillograph  as  a  dead-beat  galvano- 
meter, and  I  ran  the  oscillograph  motor  at  the  same  time  to  see 
whether  the  harmonics  of  armature  reaction  could  be  directly 
observed.  The  results  are  shown  in.  Plate  I.,  the  corresponding  con- 
ditions being  given  in  Table  IX.*    These  curves  are  records  of  the 

•  The  letters  N,  E  ;  U,  E,  etc.,  in  the  top  row  of  numerals  indicate  the 
excitations  of  first  and  second  converter  respectively  for  each  vertical 
column  of  curves. 


592  THORNTON:    EXPERIMENTS   ON  [Newcastle, 

rapid  magnetic  changes  occurring  within  the  core  when  this  is  worked 
at  various  saturations  and  with  different  values  of  armature  reaction. 
They  are,  in  effect,  the  voltage  in  the  secondary  coil  of  a  transformer 
of  which  the  magnetic  frame  is  the  core  and  the  armature  the  primary. 
They  are  interesting,  as  showing,  for  the  first  time,  I  believe,  what 
kind  of  action  really  goes  on  within  the  magnetic  circuits  of  these 
machines,  and,  I  have  reason  to  think,  of  all  kinds  of  dynamo-electric 
machinery,  for  I  have  obtained  similar  curves  (Fig.  19)  from  con- 
tinuous-current motors  separately  excited,  driven  from  cells,  and 
running  light.  The  most  curious  point,  I  think,  about  the  curves  is 
the  absolute  constancy  of  form  observed,  except  when  a  phase  swing 
starts.  All  the  ripples  remain  steady,  and  the  curves  can  always  be 
repeated.  The  same  applies  to  the  records  of  Plate  I.  This  method 
of  examination  seems  to  me  to  afford  a  most  delicate  test  of  whether 
the   armature  is  perfectly  symmetrical  in  the  gap,  and    should  be 

OeNERATED  VOLTAOC 

1120  R.RM 

.-?'^y.'!!?.J.    -  -  '^-^"'^^ -L  /r'  ^  WfTH     I      HELD 

COIL  VOLTAGE  f  \  ^  /  5.4  AMP&/  CURRENT 

Scott  &  Mountain. 


COIL  VOLTAQg    s/  M?     W     W  V     ^  3*      "       '  CURRENTS 

Holmes. 

GENERATED  VOLTAGE 

Fig.  19.— Oscillations  of  Magnetic  Fluids,  in  Separately  Excited  Continuous- 
Current  Motors  Running  Light. 

useful  in  the  study  of  flicker,  or  to  indicate  the  magnitude  of  the  dis- 
turbances, mechanical  or  magnetic,  caused  by  the  armature  running 
out  of  truth.  The  records  of  Plate  I.  are  no  doubt  complicated  by  the 
presence  of  these  oscillations,  especially  the  more  rapid  movements  in 
the  three-phase  curves. 

A  detailed  analysis  of  the  curves  in  Plate  I.  would  be  very  laborious, 
but  some  general  conclusions  may  be  drawn.  Taking  the  first  converter 
single-phase  set  first  (curves  i6  to  20  in  Plate  II.),  it  is  seen  that  the  light 
load  losses  are  practically  the  same  for  all  excitations,  and  that  over- 
excitation more  than  doubles  them  for  the  same  load,  for  the  ampli- 
tudes of  the  curves  are  much  the  same,  and  the  strip  resistance  was 
i6*i  ohms  in  16,  but  only  6*1  in  20.  The  first  three  and  20  show  a 
change  of  phase  of  the  harmonic  of  about  45  deg.,  backward  in  16,  18, 
and  20,  forward  in  17.  Under-exciting  the  first  machine  causes  the 
harmonic  to  lag  with  respect  to  the  voltage  more  than  in  the  other 
cases.      This  double   frequency  harmonic    alternately   weakens    and 


1902.  J 


SYNCHRONOUS   CONVERTERS. 


593 


strengthens  the  flux  in  the  gap,  and  this  can  be  seen  by  19,  where 
it  is  in  the  first  half  opposite  to  and  in  the  second  in  phase  with  the 
voltage.  The  motor  reaction,  curves  i  to  5,  shows  a  remarkably  con- 
stant type ;  there  is  a  quadruple  harmonic  present,  and  the  phase  of 
this  is  moved  i8o  deg.  of  its  own  between  3  and  5.  The  reason  for  the 
existence  of  these  still  higher  waves  and  the  meaning  of  this  shift  of 
phase  I  have  not  had  the  time  to  examine  more  fully,*  but  it  is  of 
interest  to  see  that  the  same  changes  occur  in  the  three-phase  curves, 
and  that,  as  before,  the  losses  are  greatest  with  an  over-excited  first 
converter. 


Table  IX. 


- 

Curve. 

I 

Single- 
phase     - 
(Holmes) 

2 

3 
4 
5 

Three- 
phase 
(Holmes) 

'       6 

I 

9 
10 

Three- 
phase 
(Scott 
and 
Mountain) 

'     II 
12 
13 
14 
15 

Single-      / 

'     16 

f>hase 

Scott      K  xu 

and        1 1  19 

Mountain)  \^!  20 


ist  conv. 

and  conv. 

Field 

Field 

Current. 

Current 

2 

1-93 

2 

272 

2 

329 

v6 

27 

3*1 

27 

1-9 

362 

19 

2*4 

19 

1-95 

r6 

27 

3*1 

27 

19 

362 

1*9 

2*4 

1-9 

1*95 

1-6 

27 

3*1 

27 

2 

19 

2 

27 

2 

3*2 

1-6 

27 

1      3 

27 

Total  ohms  in  strip 

2nd  conv. 

circuit. 

1 

Con.  cur. 

Revs. 

output. 

1 

Light. 

Loaded. 

1 
! 

28 

2I'I 

2I-I 

1,150 

32 

211 

2I-I 

1,000 

34*5 

61 

23*1 

i»o75 

22 

13-1 

23-1 

1, 000 

3i'5 

29-1 

33*1 

1,020 

34 

3*1 

4*1 

1,000 

417 

4*1 

f' 

1,020 

30 

4*1 

6-1 

1,000 

20 

21 

2*1 

1,000 

29 

in 

III 

1,000  , 

33 

21 

21 

1 
900 

39*5 

2*1 

8-1 

1,030 

30 

21 

4*1 

1,000 

20 

2*1 

2*1 

1,050 

20 

2-1 

2-1 

1,000  1 

24 

4*1 

161 

1,060 

20 

4*1 

141 

1,080 

30 

4*1 

91 

1,060 

non-p. 

61 

6-1 

1,060 

15/25 

61 

6-1 

840 

To  return  to  the  determination  of  the  ampere-turns  of  reaction. 
Let  t%be  the  voltage  generated  in  the  exploring  coil,  as  found  by  a  hot- 
wire galvanometer  or  from  the  curves,  and  let  there  be  s  turns  on  the 
coil.  Then,  when  /  is  the  frequency  of  oscillation  (which  will  not  be 
simply  that  of  the  machines  if  there  are  harmonics), 

er  =  4  N/s/io*, 
•  It  varies  with  both  excitation  and  load. 


694  THORNTON:    EXPERIMENTS  ON  [Newcastle, 

where  N  is  the  mean  flux  through  the  coil.  Here  e  is  root  mean  square, 
and  N  an  ordinary  average,  hence  the  true  value  of 

N  =  4-.'^.io«. 
4/s    707 

but  s  is  58  on  the  Holmes  machine,  55  on  the  Scott  and  Mountain,  and 
/  and  e  are  observed ;  thus  N  is  known.  Now,  N  =  Magnetomotive 
force/reluctance.    Thus  writing 

XT        4  IT   I  /    . .  X  ,,  N  R 

N  =  i-  — -,  the  ampere-turns  1  /  = 

10    K*  *  1 257 

The  maximum  value  for  sine  waves  is  1*57  times  this.    Therefore 

(IT)=r25NR. 

For  the  Holmes  machine,  R  =  '005,  as  found  from  the  magnetisa- 
tion curve  for  27  amperes,  so  that 

(It)  =  2,420^//; 

and  when  the  speed  is  1,000  revolutions  per  minute, 

(I  T)  =  146  per  volt  in  the  exploring  coil. 

For  this  machine  the  mean  length  of  solid  iron  core  is  loocm.,  the 
radius  7*8cm.  Taking  the  specific  resistance  as  10,000,  and  the  per- 
meability as  100,  the  watts  lost  at  1,000  revolutions  per  minute  are 
I2S  per  100  maximum  ampere-turns.*  Thus  we  have  finally,  since  the 
loss  depends  on  the  square  of  the  reaction  ampere-turns,  266  watts  per 
volt.  Considering  the  double  frequency  harmonic,  this  loss  is  reduced 
from  266  to  65  watts.  When  there  is  little  or  no  phase  swinging,  the 
voltage  is  from  two  to  three  at  medium  loads.  The  oscillograph  cali- 
bration was  2' I  cm.  deflection  per  volt  with  lo'i  ohms  in  circuit,  from 
which  the  amplitudes  of  Plate  I.  may  be  worked  out  in  volts.f  Taking 
an  equivalent  sine  maximum  of  2*5  volts,  with  the  double  frequency 
harmonic  of  Curve  2,  there  are  102  watts  lost  by  eddy  currents  in  the 
magnet  core.  It  will  be  seen  from  Fig.  12  that  this  accounts  for  a  good 
deal  of  the  discrepancy  between  the  observed  and  calculated  loss  in  the 
Holmes  machine,  and  I  think  that  all  the  wide  differences  are  due  to 
the  same  cause. 

§  6.  Effect  of  Armature  Reaction  on  Wave-Form, — ^The  relation 
between  excitation  and  phase  displacement  has  been  shown  in 
Figs.  4,  5,  and  6.  These  were  verified  by  direct  observation  in  the 
oscillograph  and  the  waves  sketched.  The  voltage  curve  remains 
singularly  constant  in  shape  under  all  conditions,  but  the  current 
wave,  depending  as  it  does  on  the  phase  relations  of  the  two  machines, 
is  very  sensitive  to  changes  in  the  magnetic  circuits.  The  chief  cause 
of  the  variation  of  form  is  the  harmonic  of  armature  reaction,  and  the 
phase  of  this  changes  considerably  with  regard  to  the  main  wave. 

•  Magnetic  leakage  reduces  the  intensity  of  the  eddy  currents  towards  the 
yoke,  thus  diminishing  the  loss,  but  the  working  permeability  is  about  400, 
and  the  eddy  current  loss  is  directly  proportional  to  this. 

t  The  curves  as  printed  arc  about  quarter  full  size. 


1902.] 


SYNCHRONOUS  CONVERTERS. 


595 


Plate  II.  contains  a  selection  from  the  wave-forms  sketched.  The 
current  curves  of  Plate  II.  are  not  all  to  the  same  scale.  Tables  V., 
VI.,  and  IX.  give  the  true  values.  Curves  i  to  22 a  are  for  a  single- 
phase  working,  the  rest  for  three-phase.  On  all  the  curves  but  22  and 
22.\  the  conditions  of  excitation  are  indicated  by  the  letters  O  E,  U  E,  or 
N  E,  signifying  over,  under,  or  normal  excitation.  In  14A  the  phase  dis- 
placement from  lag  to  lead  as  the  excitation  is  increased  in  the  second 
converter  is  shown  ;  22  gives  the  magnitude  and  nature  of  the  wave 
changes  during  moderate  phase  swinging,  and  22A  is  the  single  curve* 
in  which  the  brushes  have  been  moved  from  mid-position,  A„  corre- 
sponding to  a  slight  backward  shift,  and  A,  to  the  extreme  backward 
shift  when  the  sparking  was  too  heavy  to  be  long  continued.  The  first 
set,  from  i  to  6,  were  taken  after  the  readings  of  Table  IV.  These 
were  approximately  repeated,  as  in  Table  X.,  to  which  the  curves 
correspond.  In  these  the  full  effect  of  change  of  excitation  can  be 
seen  both  on  form  and  phase.  The  strong  harmonic  of  Curve  i  always 
appears  when  the  second  machine  is  fully  excited  and  the  field  of  the 
first  gradually  reduced,  the  speed  being  maintained  constant  by 
varying  the  armature  current.  The  lateral  shift  of  the  harmonic  is 
most  marked  from  i  to  2,  the  other  curves  showing  chiefly  a  variation 
in  its  amplitude. 

Table  X. 
Field  Current  of  First  Converter,  2  Amperes  ;  Second,  37  Amperes. 


No.  of    • 
Curve. 

First  Converter 
input 

Second  Converter  input. 

Second  Con- 
verter output. 

v. 

A. 

V. 

A. 

w. 

Cos0. 

V. 

A. 

I 
2 

t. 

37 

62 

54*5 

13-6 
40 

532 
2,190 

•65 
10 

0 

79 

0 

19*5 

Field  Current  of  First  Converter,  2  Amperes ;  Second,  7  Amperes. 


3 
4 


80 

357 

48 

39*5 

1,910 

I 

68 

82 

13-5 

52-4 

20*5 

472 

•44 

0 

19-4 

o 


Field  Current  of  First  Converter,  2  Amperes ;  Second,  2  Amperes. 


^ 

16 
30 

45*6 

30 

37*5 


504 
1484 


•35 
•87 


o 
61 


o 

15 


Curves  7  to  21  were  taken  simultaneously  with  the  readings  of  Table 
v.,  as  indicated,  and  it  is  of  interest  to  trace  the  nature  of  the  change 
with  load  in  each  case  of  excitation.  In  11,  for  example,  the  current 
being  more  than  double  that  of  7,  the  harmonic  has  moved  over  60°  and 
its  amplitude  increased. 


696  THORNTON:    EXPERIMENTS  ON  [Newcastle, 

The  curves  from  23  to  40  are  for  three-phase  working,  and  partly 
correspond  to  Table  VI.  In  the  last  eight  the  first  machine  was  driven 
mechanically  by  belting,  but  the  differences  between  these  and  the  pre- 
vious nine  are  not  important.  It  is  evident  that  the  field  distortion  is 
extremely  small  when  working  three-phase  compared  with  single-phase. 
With  the  exception  of  a  weak  third,  harmonics  are  almost  absent.  There 
is  a  slight  distortion  of  the  field  as  in  a  continuous-current  motor,  which 
is  met  in  practice  by  suitable  brush  displacement,  but  phase-swing  is 
difficult  to  start,  and  is  not  maintained  to  the  same  extent  as  in 
single-phase  running. 

It  may  be  concluded  from  these  experiments  that  over-excitation  of 
the  second  machine  or  motor  improves  the  stability  of  the  system,  but 
that  if  the  generator  or  first  machine  is  under-excited,  although  the  ratio 
of  the  flux  densities  in  the  gaps  may  be  kept  constant,  there  will  be  both 
an  increase  in  the  eddy-current  losses  and  in  the  instability  of  working  by 
reason  of  phase  swinging.  It  is  more  economical  then  to  expend  energy 
in  over-excitation  than  to  allow  phase  swing  to  start  and  stop  it  by 
damping  coils.  These  are  necessary  in  any  case  where  there  is 
a  periodic  irregularity  in  the  generator  speed,  but  they  depend  upon 
a  well-marked  change  in  the  magnetic  circuit,  and  when  this  is  saturated 
the  magnitude  of  the  disturbance  is  less. 

Eddy  currents  in  continuous-current  machinery  have  been  previously 
thought  of  as  almost  entirely  located  in  the  armature  and  pole-faces. 
From  these  tests  it  is  seen  that  with  a  periodic  oscillation  through  the 
whole  magnetic  circuit  the  losses  in  the  solid  cores  are  considerable, 
and  I  believe  that  the  greater  part  of  the  eddy-current  loss  found  by  any 
of  the  usual  tests  takes  place  in  the  solid  frame.  If  this  is  to  be  prevented, 
the  mechanical  construction  must  be  as  accurate  as  in  engine  fitting. 
The  pole-faces  must  be  bored  smooth  and  set  to  gauge.  The  armature 
must  be  as  true  as  a  gun  barrel  and  perfectly  centred.  Its  shaft  must  be 
stiff  enough  to  prevent  the  least  bending  and  must  not  whirl  at  any 
speed,  for  the  most  violent  magnetic  changes  will  be  set  up  if  this  occurs. 
If  it  is  attached  to  overhung  pulleys  or  flywheels,  which  cause  bending, 
these  must  be  compensated  as  in  a  balanced  engine.  Of  course,  all  this 
is  if  it  is  worth  doing.  It  is  merely  a  question  of  first  cost — the  user 
pays  for  the  energy  lost  in  the  damping  system. 

I  hope  that  these  experiments  will  be  preliminary  to  others  on  sub- 
station machines  under  working  conditions,  and  a  rather  lengthy  scries 
of  tests  on  the  effect  of  brush  position  on  efficiency  and  wave-form  has 
already  been  made.  I  think  it  will  be  admitted  that  our  e.xpcrimental 
knowledge  of  the  reactions  in  alternators  and  converters,  and  in 
continuous-current  machinery  also  when  subject  to  changes  in  the 
mechanical  torque,  is  at  present  imperfect.  I  venture  to  hope  that  the 
experimental  methods  of  studying  the  changes  in  the  magnetic  circuits 
given  in  this  and  last  session's  paper  *  will  contribute  a  little  to  a  more 
thorough  knowledge  of  what  really  goes  on  within  both  fields  and  arma- 
tures of  dynamo-electric  machines  in  general,  and  lead  to  an  improve- 
ment in  their  efficiency  and  stability  of  working. 

•  The  Electrician^  May  30  and  June  13,  1902  ;  the  Electrical  Engineer^  April 
and  May,  1902. 


1902.]  SYNCHRONOUS   CONVERTERS  :    DISCUSSION.  597 

Mcr  John  H.  Holmes  (Chairman)  said  that  the  Institution  was  highly  Mr.  Holmes, 
favoured  to  have  had  such  an  important  paper  read  before  it. 
Dr.  Thornton's  previous  paper  had  been  of  very  great  interest  and  this 
was  a  continuation  of  it,  while  the  points  he  had  now  brought  out  were 
very  interesting.  It  had  probably  been  recognised,  to  some  extent,  that 
changes  took  place  in  the  field  magnets  of  continuous-current  dynamos 
when  there  was  something  wrong  with  the  armature,  if  it  was  very 
much  out  of  balance,  or  if  there  was  a  short  circuit,  but  we  had  no  idea 
as  to  what  those  changes  actually  were.  The  methods  introduced  for 
detecting  changes  in  these  magnets  were  very  ingenious,  and  seemed  to 
make  the  thing  much  clearer.  The  question  of  rise  in  voltage  on  field 
coils  of  dynamos  had  certainly  been  observed  and  had  led  to  inquiry. 
It  was  quite  possible  that  the  extraordinary  rise  in  voltage  noticed  on 
shunt  windings  when  the  armature  was  very  much  out  of  balance,  or 
what  the  Americans  call  the  "  bucking  "  of  dynamos,  might  find  some 
explanation  in  this  paper. 

Mr.  G.  Ralph,  after  congratulating  Dr.  Thornton  on  his  excellent  Mr.  Ralph. 
paper,  said  that,  unfortunately,  his  knowledge  of  the  subject  was  so 
slight  that  he  could  not  criticise  any  portion  of  the  paper,  but  he  had  no 
doubt  that  many  others,  like  himself,  had  occasionally  in  the  course  of 
their  work,  met  with  some  phenomenon  which  was  puzzling  at  the 
time,  and  for  which  they  could  not  find  any  explanation.  Cases  like 
these  should  be  taken  to  friends  like  Dr.  Thornton  to  be  solved. 

It  might  be  interesting  to  them  to  describe  a  curious  effect  which  came 
under  his  notice  a  few  years  ago.  He  was  engaged  in  carrying  out 
some  efficiency  trials  of  direct-coupled  engines  and  single-phase 
alternators  at  a  Corporation  Supply  Station  in  the  South  of  England. 
The  conditions  were  as  follows  : — The  engine  was  a  double-cylinder 
single-acting  engine.  The  revolving  armature  was  of  the  disc  type, 
with  no  iron  in  it,  of  the  well-known  type  made  by  Siemens,  Ferranti, 
and  others.  The  alternator  field  was  separately  excited.  When  the 
machine  was  running  with  no  current  in  the  armature,  the  potential  across 
the  exciting  terminals  of  the  field  was  80  volts,  and  the  exciting  current 
agreed  with  this  potential  difference  and  the  resistance  of  the  field. 
When,  however,  load  was  put  on  and  full  current  was  flowing 
through  the  alternator  aimature,  the  potential  across  the  exciting 
terminals  rose  50  per  cent,  or  more,  although  everything  remained  exactly 
the  same  as  before,  that  is,  the  speed  of  the  alternator  and  exciter  was 
unchanged,  the  exciting  current  and  resistance  in  the  circuit  remained 
unchanged  and  yet  the  mere  fact  of  putting  load  on  the  alternator 
caused  the  exciting  voltage  apparently  to  increase  to  this  degree.  When 
this  was  first  noticed  it  was  concluded  that  the  voltmeter  had  gone 
wrong.  It  was  an  electro-magnetic  type  of  instrument.  This  was 
taken  off,  and  a  Cardew  hot-wire  voltmeter  and  also  a  Kelvin  multi- 
cellular electrostatic  voltmeter  substituted  with  exactly  the  same  result. 
A  similar  effect  was  noticed  the  following  day  on  the  trial  of  a  smaller 
alternator.  When  he  returned  to  the  works  after  these  trials  were  over 
he  tried  to  get  the  same  effect  on  other  alternators  in  the  place— at 
the  time  in  the  course  of  construction — ^and  failed  utterly.  Some  doubt 
was  then  cast  on  his  figures,  and  the  engineer  in  charge  of  the  station 


THORNTON:    EXPERIMENTS  ON 


[Newcastle, 


Mr.  Ralph, 


Mr. 
Hcaviside. 


Mr.  Eugene- 
Brown. 


IV. 
Thornton. 


where  the  efifect  had  been  noticed  was  written  to  and  asked  to  try  again 
and  his  (Mr.  Ralph's)  figures  were  repeated  every  time.  He  would  like 
to  ask  Dr.  Thornton  if  he  thought  an  effect  like  this  would  be  produced 
by  armature  reaction  causing  a  very  strong  fluctuation  in  the  field 
magnet  cores.  He  believed  that  in  these  particular  alternators  the  field 
was  fairly  weak,  which,  as  pointed  out  in  the  paper  just  read,  would 
magnify  any  evil  of  this  sort.  He  had  never  heard  a  satisfactory 
explanation,  and  thought  it  might  be  interesting  to  mention  the  case. 

Mr.  A.  W.  Heaviside  then  proposed  a  vote  of  thanks  to  Dr.  Thornton, 
and  in  suggesting  a  visit  to  the  dynamo  room  of  the  college,  said  it 
would  be  very  profitable  to  see  the  actual  experiments. 

Mr.  E.  Eugexe-Brown  seconded,  adding  that  he  was  well  acquainted 
with  the  subject  itself,  and  was  sure  the  experiments  with  the  oscillo- 
graph would  be  full  of  interest. 

[The  members  then  proceeded  to  the  dynamo  room,  where  Dr. 
Thornton  went  through  and  explained  the  experiments,  and  also 
answered  the  questions  which  were  put  to  him. 

The  discussion  was  continued  informally  in  the  engine  room  while 
the  experiments  were  being  shown.  The  curves  of  Plate  I.  were  pro- 
jected from  the  oscillograph  on  to  a  screen,  and  the  change  from  one 
to  the  other  condition  made  gradually  by  the  field  rheostats.  Periodic 
movements  in  the  curves,  due  to  phase  swinging,  were  started  by 
throwing  load  on  and  off  the  second  converter.  Messrs.  Holmes, 
Heaviside,  Snell,  and  Ralph  took  part  in  the  discussion,  and  in  reply  to 
them  the  following  points  were  brought  out  by  Dr.  Thornton  : — ] 

Dr.  W.  M.  Thornton  :  It  is  not  possible  to  prevent  armature  reaction 
itself,  and  it  is  therefore  necessary  to  check,  in  every  possible  way,  the 
communication  of  disturbance  to  the  magnetism.  This  may  be  done  in 
any  machine  by  damping  coils  surrounding  the  poles,  by  preference, 
close  to  the  armature.  These  act  most  efficiently  when  the  iron  frame 
is  solid,  and  depend  chiefly  on  the  eddy  currents  started  by  magnetic 
waves  sent  radially  into  the  core  by  the  strong  cun-ents  induced  in  them 
by  slight  changes  of  magnetism.  Since  they  are  useful  even  when  the 
iron  is  laminated  in  making  any  oscillation  more  dead  beat  by  opposing 
the  initial  change  I  would  advocate  laminating  the  magnet  frame  of  con- 
tinuous current  machines ;  for,  in  the  first  place,  it  would  diminish  eddy 
current  loss.  It  is  generally  taken  that  the  no-load  eddy  current  loss, 
which  can  be  found,  remains  substantially  the  same  at  all  loads,  but 
according  to  these  curves  this  loss  is  about  twice  as  great  at  full  load  in 
the  second  converter.  In  cases  of  parallel  running,  with  compound 
traction  macliines  for  example,  the  currents  in  the  equaliser  circuits,  and 
therefore  the  voltages  would  more  quickly  adjust  themselves.  Design 
in  general  is  simplified  by  the  accuracy  with  which  the  permeability  of 
these  plates  can  be  found. 

The  value  of  amortisseurs.  in  preventing  fluctuations  is  such  that  one 
may  reasonably  forecast  the  time  when  every  large  machine,  either 
continuous  or  alternating,  will  be  fitted  with  them,  for  though  by  the 
use  of  high-speed  engines  and  turbo-generators,  irregular  turning  move- 
ment i:>  less,  yet  the  governing  of  both  is  far  from  perfect,  and  with  the 
small    moment    of    inertia   of  the  latter,  sudden    or    periodic    load 


1902.] 


SYNCHRONOUS  CONVERTERS  :  DISCUSSION. 


599 


may  be  very  disturbing  to  the  magnetic  circuit  unless  protected 
in  this  way. 

These  fluctuations  do  not  entirely  depend  on  armature  reaction,  for 
as  shown  by  Fig.  20  they  are  obtained  in  the  exploring  coils  when  no 
current  is  passing  in  the  armature.  That  is  to  say,  they  exist  by  reason 
of  the  variation  of  the  reluctance  of  the  air-gaps  due  to  the  armatures 
running  slightly  out  of  truth.  It  is  not  possible  in  either  case  to 
observe  any  side  movement,  nevertheless,  both  armatures  must  be 
slightly  eccentric  in  the  gap  or  the  shafts  bent.  A  quadruple  harmonic 
would  be  caused  by  a  bent  shaft  or  by  the  armature  "  whirling."  The 
fact  that  the  effect  is  greatest  when  the  field  is  strongest  confirms 
this  view. 

In  Fig.  20  the  current  required  to  drive  the  oscillograph  (about 
^  ampere)  was  being  taken  from 

SCOTT  &  MOUNTAIN  jr,rLr, cu^Jf^ffn 

3  2  AAT^DffS 


the  slip-rings.  To  eliminate  the 
effect  of  this  the  first  machine 
was  used  to  give  current  for  the 
oscillograph  motor  only,  at  the 
same  time  connecting  one  strip 
to  the  exploring  coil  on  the  . 
second  machine,  which  was 
belt  driven,  and  entirely  dis- 
connected from  the  first.  The 
curves  remained  the  same 
shape  but  were  slightly  smaller. 
It  was  not  possible  to  draw  or 
photograph  them  by  reason  of 
their  slow  procession  across 
the  screen. 

With  regard  to  Table  VIII. 
the  armature  losses  are  calcu- 
lated from  the  continuous  cur- 
rent having  regard  to  the 
irregular  distribution  of  current 
in  the  conductors.  The  energy 
taken  into  or  supplied  by  the 
armature  is  a  function  of  both 
voltage  and  current,  the  energy 

flux  entering  the  conductors  from  the  surrounding  medium  at  right  angles. 
One  may  thus  follow  the  transfer  of  energy  from  the  source  of  supply 
to  the  eddies  in  the  iron  through  the  magnetic  flux  acting  as  an  elastic 
intermediary,  and  see  it  dissipated  there  without  the  armature  current 
showing  all  that  is  going  on,  though  there  will  be  inevitably  either  a 
rise  in  current  or  drop  in  voltage  whenever  the  effect  is  taking  place. 
To  obtain  a  general  expression  for  the  losses  covering  both  voltage  and 
current  changes,  is,  I  think,  impracticable,  but  by  reference  to  Table 
VI.,  curves  30  to  32,  it  will  be  seen  that  whenever  there  is  a  great 
difference  between  the  observed  and  calculated  losses  it  is  accompanied 
by  a  large  drop  in  voltage. 

In  reply  to  Mr.  Ralph's  question  the  effect  is,  I  think,  as  follows  : — 

13!)9l3ll 


Dr. 
Thornton. 


3  8   AMKffes 


HOLMES 

Fig. 


600 


THORNTON:  SYNCHRONOUS   CONVERTERS.    [Newcastle, 


Dr. 

Thornton. 


There  was  first  an  alternating  armature  reaction  superposed  on  the 
constant  excitation.  This  field  was  weak,  and  when  the  armature  was 
strengthening  the  field  the  permeability  of  the  core  would  certainly  be 
less  than  when  acting  against  the  field  magnets.  The  alternating  voltage 
induced  in  the  field  windings  depends  on  how  this  permeability  varies. 
If  it  is  simply  harmonic  no  rise  in  voltage  can,  I  think,  occur  across  the 
exciter  terminals,  but  if  it  varies  (as,  for  example,  in  the  large  wave  of 


R/se  of 
voUkSigeon 
TerminaLs, 


EMEon  fiebd  CermimLs 
due  Co  armdiUfre  redLCtion. 


EjcdCer  voLCcLge, 


curve  I  Plate  I.  in  the  paper)  with  a  pointed  top  to  the  wave,  that  is  the 
point  where  the  voltage  will  be  greatest,  for  there  the  permeability  is 
changing  most  rapidly.  In  this  case  the  induced  voltage  in  the  field 
windings  will  be  greater  above  the  line  of  exciter  voltage  than  below 
and  there  will  be  a  rise  of  voltage  at  the  terminals,  though  the  exciter 
voltage  remains  constant.  The  instrument  must  have  been  capable  of 
reading  both  alternating  and  continuous  voltage. 

I  wish  to  thank  several  senior  students  who  have  helped  me  in 
this  work. 


1902.]  PIGG:    RAILWAY   BLOCK  SIGNALLING.  601 

NEWCASTLE    LOCAL    SECTION. 

RAILWAY   BLOCK   SIGNALLING.  V^ 

By  J.  PiGG,  Associate  Member. 
{Paper  read  at  Meeting  of  Section ^  December  15,  1902.) 

The  subject  of  signalling  generally  is  of  the  most  interesting 
character  possible,  and  code  signalling  of  some  form  or  other  seems 
to  have  been  in  use  for  the  conveyance  of  intelligence  to  points  beyond 
the  scope  of  man's  vocal  organs  during  all  periods  covered  by  history. 
If  time  permitted  we  might  commence  with  a  quotation  from  Exodus, 
and  pass  on  by  easy  stages  to  the  methods  of  signalling  of  ancient 
Egypt,  the  heliograph  of  Alexander  the  Great,*  the  torchlight  signalling 
of  the  Romans,  the  adaptation  of  the  Greek  clepsydra  to  alphabetical 
signalling,  the  drum,  smoke,  and  fire  signals  of  savage  peoples,  the 
later  beacons  and  watch-towers  of  our  own  and  other  countries, 
the  revival  of  torchlight  signalling  between  the  Scottish  mainland 
and  the  Shetland  Isles  by  the  Rev.  James  Bremner  early  in  the 
eighteenth  century,  and  so  to  the  achievements  of  the  brothers  Chappe 
on  the  Continent  with  semaphore  signalling,  and  Lord  Murray's 
shutter  form  of  telegraph  in  this  country  in  the  period  immediately 
preceding  the  introduction  of  the  electric  telegraph.  It  is  interesting 
to  remember  that  although  accounts  of  the  introduction  of  the  electric 
telegraph  now  read  like  ancient  history,  yet  we  are  still  comparatively 
near  to  the  era  of  the  semaphore  telegraph.  Although  formally  adopted 
by  the  French  Directory  in  1793,  Chappe's  system  was  not  fully 
completed  in  Russia  until  1858,  so  that  there  may  be  some  here  who, 
without  being  of  a  patriarchal  age,  and  probably  taking  but  little 
interest  in  the  subject  at  the  time,  may  still  be  said  to  be  contem- 
poraries of  the  semaphore  telelegraph.f 

The  more  particular  form  of  signalling  to  which  this  paper  refers 
has  also  an  historical  side,  which  is  of  considerable  interest  to  the 
student  of  the  evolution  of  railway  signalling.  There  are,  moreover, 
other  aspects  of  the  subject  which  are  of  great  importance.  These 
are  the  statistical,  involving  consideration  of  reams  of  figures  relating 
to  the  development  of  the  system  and  its  effects  ;  the  constructional, 
with  its  sight-destroying  and  brain-puzzling  diagrams,  illustrating  the 
principles  of  design  and  the  circumstances  to  be  met ;  and  the  opera- 
tive, with  its  enormous  mass  of  detail  for  working  purposes.  All  these 
p>oints  of  view,  including  the  historical,  are  of  the  greatest  importance 

•  See  Presidential  Address  of  Sir  Henry  Mance  to  Institution  of  Electrical 
Engineers,  January  14.  1897. 

t  For  further  information  on  pre-electric  telegraphs  see  a  most  interesting 
lecture  by  Mr.  Alderman  W.  H.  Bailey  (now  Sir  W.  H.  Bailey)  at  Salford  in 
1883,  "Telegraphs  of  the  Ancients." 


602  PIGG:    RAILWAY  BLOCK  SIGNALLING.      [Newcastle. 

in  their  several  ways,  but  they  require  more  time  to  even  skim  them 
lightly  than  is  available  here. 

There  is,  however,  still  another  aspect  of  the  subject  which,  to  the 
writer,  seems  to  be  of  supreme  importance — the  effectiveness  of  the 
system — or,  in  other  words,  its  adequacy  for  the  purpose  for  which  it 
has  been  designed.  However  interesting  other  aspects  may  be,  there 
are  none  of  such  importance  as  this.  Freedom  from  failure— and  the 
consequences — is  the  touchstone  of  any  system.  When,  as  in  railway 
signalling,  the  consequences  may  be  serious,  the  necessity  for  reliability 
is  greatly  increased.  We  might  illustrate  this  aspect  of  the  subject  by 
quoting  figures  to  show  that  travelling  by  railway  is  vastly  safer  than 
by  the  old  stage  coach,  the  newer  motor-car,  or  even,  in  view  of  recent 
lamentable  occurrences,  the  electric  tram,  inasmuch  that  a  smaller 
proportion  of  travellers  are  killed  or  injured  by  the  former  than  by 
any  of  the  latter  methods.  It  is  the  present  proud  boast  of  English 
railways  that  they  have  not  killed  a  single  passenger  through  an 
accident  to  the  train  in  twelve  months,  and  such  a  record,  considering 
the  millions  carried,  is  a  magnificent  testimony  to  the  care  and  atten- 
tion devoted  by  those  responsible  for  the  organisation,  direction,  and 
operation  of  the  enormous  traffic  carried  on  our  railways.  Yet 
accidents  do  unfortunately  occur,  and,  if  I  may  so  put  it,  it  is  small 
comfort  to  the  sufferer  to  know  that  he  is  only  a  unit  in  a  small 
percentage  of  fatalities,  and  should  be  glad  that  the  percentage  is  not 
larger. 

Objects  of  Block  System. 

There  is  no  need  on  this  occasion  to  labour  the  point  of  what  is 
meant  by  the  term  "block."  Quoting  from  the  explanation  given 
with  the  standard  rules,  we  find  that  "the  object  of  the  system  of 
block  telegraph  signalling  is  to  prevent  more  than  one  train  being  in 
the  section  between  two  block  signal-cabins  on  the  same  line  at  the 
same  time,"  or  from  the  Board  of  Trade  "  Requirements  in  regard  to 
the  Opening  of  Railways "  :  "  The  requisite  apparatus  for  providing 
by  means  of  a  block  telegraph  system  an  adequate  interval  of  space 
between  ifollowing  trains,  and,  in  the  case  of  junctions,  between  con- 
verging or  crossing  trains."  These  extracts,  by  the  use  of  the  word 
"telegraph,"  seem  to  Hmit  the  term  "block"  to  the  electrical 
signalling  apparatus,  and  ignore  the  outdoor  mechanical  signals  as 
part  of  the  "  block  system."  Definitions  of  the  system  which  may  be 
deduced  from  these  quotations  seem  to  the  writer  to  be  narrow,  and 
inadequately  indicate  the  functions  of  the  two  main  classes  of  apparatus 
used  for  the  regulation  and  control  of  traffic.  Certainly  it  is  impos- 
sible to  consider  either  class  alone  in  connection  with  the  results  to  be 
obtained.  However,  one  of  tens  obtains  a  more  vivid  idea  of  a  com- 
paratively unfamiliar  subject  by  the  use  of  a  simile,  and  the  following 
quotation  from  a  popularly- written  article  in  the  Pall  Mall  Gazette 
has  at  least  the  merit  of  being  graphic,  if  incorrect :  "  The  world- 
famous  block  system,  which,  to  furnish  a  simple  parallel,  decrees  that 
no  train  may  leave  the  bottom  of  a  flight  of  stairs  until  both  tl^^  letter 
and  the  landing  beyond  have  been  guaranteed  clear," 


1902.]  PIGG:    RAILWAY   BLOCK   SIGNALLING.  603 

The  fundamental  basis  of  block  signalling  is,  therefore,  the  preser- 
vation of  "an  adequate  interval  of  space"  between  trains,  whether 
**  following,"  "  converging,"  or  "  crossing  "  ;  the  object  is  safety  ;  and 
by  convention  or  rule  or  regulation  it  is  provided  that  not  more 
than  one  train  shall  occupy  one  pair  of  rails  of  a  certain  portion  of  the 
line  at  one  and  the  same  time.  For  signalling  purposes  the  line  is 
divided  into  discontinuous  sections,  or  blocks,  and  cabins  are  erected 
at  suitable  points  in  which,  as  required  by  the  Board  of  Trade,  the 
means  of  actuation  of  all  points  and  signals  connected  with  the 
running  lines  are  assembled,  and  in  which  is  also  placed  the  electrical 
signalling  apparatus.  The  block  section  for  the  time  being  is  the 
distance  between  the  two  cabins  in  electrical  communication  with 
each  other  at  the  time.  These  two  cabins  may  not  be  the  two  nearest 
to  each  other ;  under  certain  circumstances  intermediate  cabins  may 
be  switched  out  and  become  inoperative  for  a  time.  Ordinarily  the 
space  limit  between  trains  is  the  length  of  the  block  section,  and  it  is 
never  less  than  this  ;  but  where  the  distance  is  400  yards  or  less  the 
space  limit  may  be  two  or  three  such  sections.  It  is  not  necessary 
that  the  space  limit  be  the  same  at  all  parts  of  the  line,  and,  as  a 
matter  of  fact,  no  attempt  is  made  to  obtain  uniform  distance  between 
trains.  At  some  places  it  may  be  only  a  few  hundred  yards,  and  at 
others,  again,  it  may  be  several  miles.  Nor  is  it  necessary  that  the 
space  limits  withm  any  given  portion  of  line  should  be  constant.  In 
many  cases,  as  already  alluded  to,  means  are  provided  by  which,  for 
economical  reasons,  the  sections  and  space  limits  may  be  purposely 
varied.  In  every  case,  however,  the  minimum  distance  to  be  observed 
depends  upon  traffic  considerations,  with  which  we  are  not  concerned 
here,  and  upon  the  distance  in  which  the  heaviest  and  fastest  trains 
can  be  brought  to  a  stand  on  the  gradients  obtaining.  In  some  cases 
where  there  are  heavy  gradients  wc  may  find  that  whilst  the  block 
sections  are  the  same  for  the  up  and  down  lines,  the  space  interval  is 
greater  for  the  line  with  the  falling  than  for  that  with  the  rising  gradient. 

Main  Divisions  of  Apparatus. 

A  cursory  examination  of  the  subject  shows  that  the  apparatus 
employed  in  railway  signalling  may  conveniently  be  divided  into  two 
great  classes — the  outdoor  mechanical  signals,  and  the  electrical  signal- 
ling apparatus.  The  former  are  used  for  the  actual  control  and 
regulation  of  the  movement  of  traffic ;  the  latter  is  provided  for  per- 
fecting the  arrangements  for  the  exhibition  of  the  proper  signals  for 
the  time  being,  and  is,  therefore,  an  auxiliary.  The  whole  art  of 
railway  signalling,  therefore,  consists  in  the  exhibition  of  suitable  signals 
to  the  controllers  of  trains  as  they  approach  the  sections  or  blocks. 

The  forms  of  the  mechanical  signals  in  use  in  this  country  are  well 
known,  but  there  are  one  or  two  details  respecting  them  which  may 
be  touched  upon  here.  A  certain  class  of  signal,  the  "  distant,"  may 
be  passed  when  in  the  "  on  "  position.  Its  indication  is  of  a  cautionary 
character  only  when  in  the  position  named,  and  shows  that  the  section 
ahead  has  not  been  prepared  for  the  free  passage  of  the  train,  and  that 


604  PIGG:   RAILWAY   BLOCK  SIGNALLING.      [Newcastle, 

the  driver  must  be  prepared  to  stop  at  the  next  signal  in  order,  the 
"  home."  Drivers,  however,  are  by  rule  required  to  be  prepared 
to  stop  at  any  obstruction  that  may  be  fotmd  to  exist  between  the 
"  distant "  and  the  "  home."  Naturally,  the  positions  of  "  distant " 
signals  must  be  at  such  distances  from  the  "home"  signals  as  to 
allow  any  train  to  be  brought  to  a  stand  at  the  latter  if  necessary,  and 
the  location  of  the  "  distant "  is  also  always  made  with  a  view  to  a 
clear  sight  of  it  being  obtained  as  early  as  possible  before  it  is  actually 
reached.  Other  signals  than  the  **  distant "  are  "  stop  "  signals,  which 
must  not  be  passed  by  trains  when  in  the  "on"  position,  unless 
special  permission  is  given.  Such  permission  may  be  given  by 
**  calling-on  "  signals  which  have  a  cautionary  character  when  in  the 
"  ofif "  position  ;  or  by  lamp,  flag,  or  hand  signals,  supplemented  in 
some  cases  by  verbal  and  in  other  cases  by  written  instructions. 
*  Home,"  "  starting,"  and  "  advance  "  signals  arc  all  **  stop  "  signals,  as 
are  also  siding  and  cross-over  road  signals. 

"  Stop  "  signals  have  other  characteristics  than  those  already  referred 
to.  Thus  besides  being  indicators  of  the  conditions  existing  with 
reference  to  the  continuance  of  the  journey,  they  are  also  position 
signals  in  that  they  mark  the  points  which  must  not  be  passed  by  any 
portion  of  a  train  when  the  signals  are  in  the  "  on  "  position  without 
special  permission.  They,  therefore,  are  used  to  protect  the  fouling 
points.  At  junctions  the  "home"  signals — and  the  "distants"  where 
more  than  one  are  provided — are  also  route  indicators  for  the  divergent 
lines,  since  each  such  line  is  provided  with  a  separate  "  home  *'  signal. 
These  signals  are  erected  under  the  same  rule  for  all  places,  and  the 
recognition  of  the  road  prepared,  by  drivers,  is  thereby  facilitated. 

Interlockjng  of  Points  and  Signals. 

The  means  of  actuation  of  all  signals  have  to  be  interlocked  with 
each  other,  and  with  the  means  of  actuation  of  the  points,  so  that  the 
latter  must  be  set  before  the  signals  for  them  are  lowered ;  so  that 
conflicting  signals  cannot  be  lowered  at  the  same  time  ;  so  that  points 
cannot  be  moved  when  the  signals  are  in  the  "  off  "  position  ;  and  the 
points  must,  as  far  as  possible,  be  interlocked  amongst  themselves  so 
that  risk  of  collision  is  avoided.  Cabins  must  be  so  situated  as  to 
provide  the  best  possible  view  of  the  line,  and  to  enable  the  signalman 
to  see  the  arms  and  lights  of  the  signals  and  the  working  of  the 
points.  Where  signal  arms  and  lights  cannot  be  seen  they  are  to  be 
repeated  in  the  cabin.  Facing  points  must  be  avoided  as  far  as 
possible,  and  must  not  be  more  than  200  yards  from  the  cabin,  and 
trailing  points  not  more  than  300  yards.  All  facing  points  are  to  be 
fitted  with  facing-point  locks  and  locking  bars,  and  with  means  for 
detecting  failure  in  the  connection  between  the  signal  cabin  and  the 
points.  The  length  of  the  locking  bars  must  exceed  the  greatest  wheel 
base  between  any  two  pairs  of  wheels  of  vehicles  in  use  on  the  line,  and 
stock  rails  are  to  be  tied  to  gauge  by  iron  or  steel  ties.  All  points, 
whether  facing  or  trailing,  arc  to  be  fitted  with  double  connecting  rods, 
and  must  be  worked  or  bolted  by  rods  and  not  by  wires. 


1902.]  PIGG:    RAILWAY   BLOCK  SIGNALLING.  606 

These  conditions  all  make  for  safety,  and  on  their  stringency  it  is 
unnecessary  to  comment  here.  It  is  impossible  to  over-estimate  the 
importance  of  the  interlocking  of  points  and  signals  at  important 
junctions  or  busy  centres  of  distribution.  Such  places  as  busy 
passenger  station  5rards,  whilst  they  can  be,  and  are,  worked  without 
the  ordinary  electrical  portion  of  the  block  system,  could  not  possibly 
be  worked  without  interlocking  at  anything  like  their  present  efficiency, 
or  with  the  freedom  from  accident  that  obtains  at  present.  The  inter- 
locking in  busy  yards  not  only  exists  between  the  dififerent  levers  in 
any  one  cabin,  but  there  is,  necessarily,  also  a  large  amount  of  inter- 
cabin  K:ontrol  where  a  yard  is  worked  by  a  number  of  cabins.  How 
intricate  is  the  control  which  must  be  established  will  be  readily  seen 
from  an  inspection  of  the  signalling  plan  of  any  large  station  yard. 

Power  Signalling. 

We  have,  hitherto,  considered  the  working  of  points  and  signals 
exclusively  from  the  point  of  view  of  manual  operation.  The  tendency 
to  the  use  of  power,  under  manual  control,  for  this  purpose  is  at  the 
present  moment  becoming  very  marked.  The  working  of  points  and 
signals  by  electrical  power  has,  of  course,  been  in  operation  at  Earl's 
Court  Station  on  the  Timmis  system  for  some  time.  The  Great 
Eastern  Railway  Company  has  put  down  an  installation  of  the 
Westinghouse  electro-pneumatic  signalling  system  at  Bishopsgate, 
and  the  North-Eastern  Railway  has  recently  fitted  up  two  cabins  at 
Tyne  Dock  with  the  same  system.  The  London  and  North- Western 
Railway  Company  has  put  down  a  large  installation  at  Crewe,  where 
all  the  necessary  operations  are  carried  out  by  electrical  power.  This 
system,  commonly  known  as  the  "  Crewe  "  system,  is  to  be  put  down 
at  an  important  junction  on  the  North-Eastern  Railway  at  York. 
Messrs.  Siemens  and  Halske  also  have  a  very  complete  system  of 
electrical  piower  signaUing,  installations  of  which  have  been  put  down 
at  various  places  on  the  Continent.  It  is  impossible  within  the  limits 
of  a  paper  like  this  to  enter  into  details  of  any  system,  or  even  to 
consider  their  advantages.  The  tendency  to  the  use  of  power  for  the 
purposes  alluded  to,  in  preference  to  hand  labour,  is  merely  noted  as  a 
development  which  is  just  in  its  first  stage.  Nethertheless,  it  may  be 
considered  as  certain  that  the  subject  has  received  careful  attention 
from  railway  engineers,  and  that  such  installations  would  not  be  put 
down,  even  as  experiments,  unless  there  was  a  fair  prospect  of  their 
being  successful  in  promoting  either  efficiency  or  economy. 

Electrical  Equipment  and  Operation. 

Turning,  now,  to  the  electrical  equipment  for  the  signalling  of  a 
railway,  we  find  a  large  number  of  matters  of  great  importance  which 
the  time  available  will  not  allow  of  discussing.  Such  points  are  the 
signalling  of  single  lines,  and  the  particular  conditions  to  be  complied 
with;  the  use  of  permissive  systems  of  signalling,  with  recording 
instruments  for  certain  classes  of  line ;  the  employment  of  the 
telegraph  and  the  telephone  as  auxiliaries  in  train  signalling ;  gate- 


606  PIGG:    RAILWAY  BLOCK  SIGNALLING.      [NewcasUe, 

crossing  equipments  ;  the  repeating  of  signals,  lights,  points,  etc. ;  the 
apparatus  used  to  indicate  when  trains  or  vehicles  are  standing  at  a 
signal  which  is  out  of  sight  of  the  signalman,  or  where  the  line  is  not 
clearly  visible  ;  rail  treadles  or  insulated  rails  and  their  uses,  or  other 
special  devices  which  go  to  make  a  complete  system.  We  have  not 
even  time  for  an  analysis  of  the  codes  and  regulations  under  which 
signalling  is  carried  on ;  for  a  discussion  of  the  relative  merits  of  three- 
wire  or  one-wire  systems;  or  for  the  much-debated  question  of  the 
best  form  of  instrument,  from  either  the  electrical  point  of  view  or  from 
the  operator's  standpoint.  The  latter  question  is  quite  as  easy  of  settle- 
ment as  the  question  of  the  best  arc  lamp  or  the  best  motor,  municipal 
versus  private  trading,  provision  for  the  depreciation  of  plant,  or  any  of 
the  numberless  matters  on  which  many  people  agree  to  differ  more  or 
less  amicably. 

The  electrical  equipment  for  a  block  section  is  very  simple,  but  the 
amount  of  apparatus  to  be  provided  at  any  block  station  depends  upon 
the  character  and  importance  of  the  place.  If  we  take  the  simplest 
example  of  such  a  station,  say  a  mere  passing  place,  we  shall  find  that 
where  single-needle  apparatus  is  employed  the  equipment  will  consist 
of  two  bells  and  four  such  instruments.  One  bell  and  two  instruments 
will  be  in  electrical  communication  with  the  block  station  on  the  up 
side  of  the  cabin  considered,  and  the  remainder  in  connection  with  the 
cabin  on  the  down  side.  The  bells  are  for  the  purpose  of  giving  and 
receiving  information,  or  for  the  making  of  arrangements  in  accordance 
with  the  voluminous  code  which  provides  for  all  circumstances 
that  may  arise  in  connection  with  the  working  of  traffic.  The  instru- 
ments are  also  used  to  a  slight  extent  in  connection  with  the  code,  but 
they  have  other  and  more  important  duties  to  perform,  in  that  they  are 
intended  to  indicate  continuously  the  condition  of  the  lines  of  rail 
they  represent.*  There  are  numerous  forms  of  block  instrument  in  use, 
each  embodying,  no  doubt,  its  designer's  idea  of  the  best  method  of 
performing  the  desired  operations,  but  with  constructional  details  we 
are  not  at  present  concerned,  and  so  far  as  their  indications  are  con- 
cerned they  are  all  alike  in  that  they  represent  the  condition  of  the  line 
by  convention  only. 

A  study  of  the  code  and  regulations  for  the  working  of  traffic  shows 
that  there  arc  three  conditions  of  the  line  which  the  block  instrument 
should  indicate.    These  are  : 

"Line  Blocked,"  "Line  Clear,"  and  "Train  on  Line." 
The  first  is  the  indication  to  be  given  when  the  section  is  clear  of  trains 
altogether ;  the  second  is  the  indication  required  when  the  section  has 
been  prepared  for  a  train,  but  which  has  not  yet  entered  the  section  ; 
the  third  is  the  indication  provided  to  show  that  a  train  is  actually 
passing  between  the  two  block  stations.  Each  of  these  indications  is 
"  permanent,"  in  the  sense  that  it  is  required  to  be  exhibited  during 
the  whole  time  the  condition  it  represents  continues ;  the  indications 
on  the  two  instruments  representing  a  line  of  rails,  in  the  two  cabins, 

•  On  the  N.E.R.  the  use  of  the  indicators  in  conneclion  with  the  code  has 
been  discontinued  since  the  paper  was  read. 


1902.]  PIGG:    RAILWAY  BLOCK  SIGNALLING.  607 

are  the  same,  and  the  indications  are  under  the  control  of  and  made  by 
the  man  towards  whom  the  train  signalled  is  proceeding — i.e.,  at  the 
exit  of  the  section. 

The  operations  necessary  to  the  passage  of  a  train  may  be  briefly 
described,  it  being  premised  that  the  character  of  the  train  is  immaterial 
for  the  present  purpose.  Suppose  a  train  is  approaching  station  "  C  *' 
on  the  up  line  and  will  pass  on  to  "  D."  Station  "  C  askes  station  "  D" 
by  code  "  Is  line  clear  ? "  (there  are  1 1  variants  of  this  signal).  If  the 
train  may  proceed,  "  D "  replies  by  code  to  that  efifect,  and  gives  an 
indication  on  the  block  instrument  for  the  up  line  at  his  own  station  and 
at  "  C,**  which  reads  "  Line  clear."  This  indication  remains  until  a 
further  stage  of  the  operations,  and  serves  as  a  continual  reminder  to 
"  D  "  that  he  has  given  permission  for  a  train  to  leave  "  C,"  and  to  the 
signalman  at  the  latter  station  it  serves  as  a  continuous  reminder  that 
he  has  obtained  permission  to  forward  a  train.  Under  the  conditions 
now  obtaining  the  signalman  at  "  C  "  may  place  his  mechanical  signals 
in  the  "  off  "  positions  to  allow  the  train  to  proceed  to  "  D." 


When  the  train  is  leaving  "  C  "  the  signalman  there  sends  the  "  Train 
entering  section  "  bell  signal  to  "  D,"  who  must  acknowledge  it  and 
change  the  position  of  the  block  indicators  in  his  own  and  "C's  "  cabin 
for  that  line  to  "  Train  on  line,"  and  this  indication  serves  as  a  con- 
tinuous reminder  to  both  signalmen  that  there  is  a  train  in  the  section. 
When  the  train  has  passed  "  D "  and  gone  forward  under  precisely 
similar  conditions,  the  signalman  there  advises  '*  C  "  that  the  section  is 
again  clear  by  giving  the  *'  Train  out  of  section  "  dial  signal,  and  leaves 
the  needle  of  the  block  instrument  in  the  "  Line  blocked  "  position.  In 
the  diagram  the  various  conditions  may  easily  be  followed. 

Relative  Responsibility  of  Signalmen. 

If  we  consider  the  functions  of  the  two  signalmen,  we  find  that  for 
traffic  in  one  direction  one  of  them  is  more  responsible  than  the  other. 
The  signalman  at  the  exit  is  the  person  who  gives  permission  for  a  train 
to  "enter  the  section,  and  before  doing  so  he  must  assure  himself  that 


608  PIGG :    RAILWAY  BLOCK  SIGNALLING.      [Newcastle, 

the  conditions  obtaining  are  suitable.  Further,  he  must  arrange  for  its 
disposal  on  arrival  at  his  cabin,  and  see  that  it  is  in  such  condition  as 
will  justify  him  in  clearing  the  section  after  it  has  passed  out.  The 
signalman  at  the  entrance  to  the  section  cannot,  under  normal  circum- 
stances, authorise  a  train  to  proceed  without  having  obtained  the  permis- 
sion given  by  the  acknowledgment  of  the  "  Is  line  clear  ? "  signal,  and 
the  giving  of  the  "  Line  clear  "  indication.  Hence  the  responsibility 
for  the  authorised  progress  of  the  train  rests  with  the  signalman  towards 
whom  the  train  is  proceeding.  The  signalman  at  the  entrance  becomes 
the  guardian  of  the  section,  and  must  protect  against  the  entrance  of  a 
train  by  the  exhibition  of  the  proper  signals.  For  ordinary  double-line 
working  one  signalman  is,  of  course,  the  sender  for,  say,  the  up  line  and 
the  receiver  for  the  down  line,  so  that  responsibility  is  averaged  for  the 
total  traffic. 

If  we  carefully  consider  the  relationship  existing  between  the  two 
divisions  of  apparatus,  we  find,  as  already  stated,  that  the  electrical  is 
an  auxiliary  to  the  mechanically-operated  outdoor  signals,  and  exists 
for  the  purpose  of  perfecting  arrangements  for  the  safe  dispatch  of 
traffic  between  persons  charged  with  its  control,  situated  at  considerable 
distances  apart,  for  the  purpose  of  indicating  the  condition  of  the  line 
between  those  persons  at  all  times,  according  to  fixed  conventions  or 
rules,  and  for  the  notification  of  its  passage  from  point  to  point.  The 
safety  of  the  system  consists  in  the  actions  of  all  parties  to  the  movement 
of  trafi&c  being  synchronised,  and  as  this  most  important  point  is  only 
possible  by  the  aid  of  the  electrical  equipment,  its  value  as  an  adjunct  is 
extremely  great. 

If  we  look  over  the  requirements  of  the  Board  of  Trade  with 
reference  to  the  electrical  portion  of  the  signalling  apparatus,  we  are  at 
once  struck  with  their  meagre  character  as  compared  with  the  require- 
ments for  interlocking.  The  first  requirement  reads  :  "  The  requisite 
apparatus  for  providing,  by  means  of  the  block  telegraph  system,  an 
adequate  interval  of  space  between  following  trains,  and  in  the  case  of 
junctions  between  converging  or  crossing  trains."  Then,  curiously 
enough,  under  the  head  of  "  Interlocking,"  we  have  :  "  The  signal  cabin 
to  be  commodious,  and  to  be  supplied  with  a  clock  and  with  a  separate 
block  instrument  for  signalling  trains  on  each  line  of  rails." 

If  we  contrast  the  wording  of  the  requirements  with  reference  to 
the  operation  of  the  two  classes  of  apparatus,  we  cannot  fail  to  observe 
the  great  difference  in  the  degree  of  precision  in  the  language  employed. 
Referring  to  the  requirements  with  regard  to  interlocking,  we  find  that 
the  signalman  "  shall  be  unable  "  to  lower  a  signal  until  after  the  points 
are  set  for  the  road  controlled  by  that  signal ;  that  "  it  shall  not  be 
possible  "  for  him  to  exhibit  signals  which  will  give  rise  to  a  collision  ; 
and  that  "  he  shall  not  be  able  "  to  move  points  connected  with  a  line 
the  signals  for  which  have  been  previously  lowered.  There  is  no 
similar  precision  in  the  requirements  for  the  electrical  apparatus,  the 
references  being  as  already  quoted  :  "  The  requisite  apparatus  .  .  .  "  ; 
"  a  separate  block  instrument  for  signalling  trains  on  each  line  of  rails." 
Turning  to  the  standard  code,  we  find  the  general  regulation  to  read  : 
"  All  fixed  signals  must  be  kept  at  danger  except  when  it  is  necessary 


1902.]  PIGG:    RAILWAY   BLOCK   SIGNALLING.  609 

to  lower  them  for  a  train  to  pass  ;  and  before  any  signal  is  lowered, 
care  must  be  taken  to  ascertain  that  the  line  is  clear,  and  that  the  block 
telegraph  and  other  regulations  have  been  duly  complied  with." 

Limitations  of  Ordinary  Systems. 

If  we  consider  the  limitations  of  such  a  system  of  signalling  as  has 
been  outlined,  we  find  that  its  greatest  weakness  arises  from  the  want 
of  interdependence  between  the  two  divisions  of  apparatus.  Theo- 
retically, the  arrangements  are  perfect ;  one  signalman  acts  as  a  check 
upon  the  other  in  so  far  as  they  are  both  concerned  in  any  operation, 
and  the  interlocking  checks  inadvertent  error  in  the  operation  of  the 
outdoor  signals  at  either  block  station  in  so  far  as  fouling  routes  are 
concerned.  But  neither  signalman  has  a  complete  check  on  the  actions 
of  the  other,  and  as  the  operation  of  the  mechanical  signals  is  in  no 
way  dependent  upon  the  block  instruments,  the  operations  need  not 
necessarily  synchronise,  and  interlocking  will  not  prevent  following 
collision  where  operations  of  the  signals  may  be  repeated  without 
check.  The  sending  signalman  depends  upon  the  observation  of  the 
man  at  the  exit  of  the  section  when  the  latter  accepts  the  "  Is  line 
clear ?"  signal,  and  must  necessarily  do  so;  the  receiving  signalman 
relies  upon  the  man  at  the  entrance  to  the  section  not  to  send  trains 
into  the  section  without  the  usual  acceptance  and  subsequent  notice  of 
the  change  of  position  of  the  train,  but  is  powerless  to  control  his 
actions ;  and  both  signalmen  rely  upon  the  due  observance  by  the 
drivers  of  trains  of  the  signals  exhibited  for  their  guidance.  Hence 
there  are  three  independent  persons  engaged  in  the  movement  and 
control  of  traffic,  any  one  of  whom  by  a  dereliction  from  duty  may  be 
the  cause  of  accident.  Accid  ents  caused  by  deviations  from  the  regula 
tions  provided  for  their  guidance  have  occurred  frequently  in  each  of 
the  three  conditions  referred  to,  and  a  study  of  the  Board  of  Trade 
inspectors'  reports  show  that  by  far  the  greater  majority  of  accidents  to 
trains  occur  through  the  failure  of  one  or  other  of  the  persons  named  to 
carry  out  his  duties  in  the  manner  prescribed.  Such  failures  are  due, 
of  course,  to  those  temporary  aberrations  which,  for  want  of  more 
knowledge,  we  call  absence  of  mind,  but  which  seem  inseparable  from 
human  existence.  Carelessness,  in  the  sense  of  deviation  from  regula- 
tions, there  may  be,  but  it  should  not  be  forgotten  that  men  necessarily 
have  other  interests,  other  causes  for  thought,  and  that  those  most  capable 
of  concentrating  their  attention  are  always  more  or  less  conscious  of 
other  thoughts  obtruding  on  their  notice. 

The  object  in  contrasting  the  Board  of  Trade  requirements  with 
regard  to  interlocking  with  the  less  onerous  stipulations  for  the 
electrical  apparatus,  is  not  to  suggest  that  simifar  requirements  should 
be  imposed  with  regard  to  the  latter.  As  a  matter  of  fact,  the  railway 
companies  have,  generally  speaking,  been  much  in  advance  of  their 
obligations,  as  will  be  seen  when  it  is  stated  that,  whilst  the  Act  of 
Parliament  making  the  block  compulsory  is  dated  1889,  and  the  require- 
ments of  the  Board  of  Trade  with  reference  to  the  Act  are  dated  1892, 
the  decade  during  which  the  greatest  progress  was  made  in  installing 


610  PIGG:    RAILWAY  BLOCK  SIGNALLING.     [Newcastle, 

the  block  was  that  of  the  seventies.  Railway  companies  have  spent 
enormous  sums  in  equipping  their  lines  with  signalling  apparatus, 
which,  from  the  operating  point  of  view,  works  well  on  the  whole,  and 
which,  by  the  high  degree  of  certainty  that  it  introduces,  has  also  con- 
tributed largely  to  speedy  transit.  Naturally,  before  scrapping  their 
present  apparatus  and  incurring  the  enormous  expense  which  such  a 
course  would  involve,  they  desire  to  assure  themselves  that  any 
suggested  change  of  procedure  will  have  the  advantages  claimed  for  it. 
A  well-known  American  signalling  engineer  some  time  ago  said  that 
absolute  safety  could  only  be  assured  by  building  a  track  for  each  train 
operated.  The  most  rabid  perfectionist  would  hardly  desire  to  push 
his  requirements  so  far  as  absolute  safety  if  it  is  to  be  obtained  at  such 
a  cost.  Perhaps  the  American  gentleman  only  desired  to  indicate  that 
"  absolute  "  perfection  is  unattainable. 

Lock  and  Block. 

The  system  of  signalling  considered  is  the  manually  operated  and 
manually  controlled,  and  its  limitations  have  been  referred  to  at  some 
length.  We  may  now  briefly  consider  what  suggestions  are  available 
for  reducing  the  risks  which  experience  shows  have  to  be  run  from 
failure  of  the  controllers.  Generally,  such  systems  are  known  by  the 
not  very  appropriate  or  self-descriptive  name  of  "  lock  and  block,"  and 
they  have  as  their  object  the  union  of  the  mechanical  signals  with  the 
block  apparatus,  so  as  to  make  their  operation  interdependent,  as  far  as 
consideration  of  the  conditions  obtaining  may  seem  desirable.  In  this 
country  systems  have  been  devised,  among  others,  by  Sykes,  Spagnoletti, 
Langdon,  Saxby  and  Farmer,  Tyer,  Evans,  and  O'Donnell.  Such 
systems,  however,  form  at  present  but  a  very  small  fraction  of  the 
signalling  apparatus  in  this  country. 

We  have  seen  that  the  signalman  at  the  entrance  to  a  section  may, 
with  the  ordinary  system,  send  a  train  away  without  the  concurrence 
or  even  the  knowledge  of  the  signalman  at  the  exit.  In  order  to  pre- 
vent this,  the  signal  controlling  the  entrance  to  a  section  is  so  inter- 
locked with  the  block  instrument  at  that  end  that  it  cannot  be  lowered 
to  admit  a  train  unless  the  man  at  the  exit  has  given  *'  Line  clear,"  and 
so  accepted  responsibility.  We  know  also  that  after  sending  a  train 
away  the  signalman  at  the  entrance  may  neglect  to  replace  his  signals 
to  danger,  and  so,  under  certain  circumstances,  admit  a  following  train. 
To  prevent  this,  a  complete  lock-and-block  system  provides  that  a  train, 
after  passing  the  signal  controlling  entrance  to  the  section,  shall 
automatically  put  that  signal  to  danger,  and  so  protect  itself  if  the 
signalman  neglects  to  do  so.  Replacement  of  the  signal  lever  in  the 
normal  position  for  dzyjger  results  in  it  being  locked  by  the  block 
instrument,  which  prevents  it  being  used  again  until  another  "  Line 
clear  "  signal  is  given  from  the  exit.  We  have  also  noted  the  fact  that, 
with  the  ordinary  system,  the  signalman  at  the  exit  can  give  "  Train 
out  of  section"  for  one  train  and  "  Line  clear"  for  one  following,  quite 
irrespective  of  the  actual  condition  of  the  section,  and  before  the  first 
train  is  out.  To  remedy  this  the  instrument  controlling  the  indications 
at  both  cabins  is  arranged  to  lock  itself  by  the  operation  necessary  to 


1902.]  PIGG:    RAILWAY   BLOCK  SIGNALLING.  611 

give  "  Line  clear."  This  lock  is  maintained  until  the  train  so  signalled 
has  passed  the  signal  controlling  entrance  to  the  next  section,  or  has 
otherwise  been  disposed  of.  Hence  we  see  that  the  operations  of  the 
signalman  are  cyclic,  and  are  intended  to  be  made  in  a  given 
order.  Further,  we  see  that  the  operations  of  the  signalman  are 
checked  on  the  points  where  risks  of  error  exist  in  the  uncontrolled 
^sterns. 

Whilst  the  union  of  the  signals  and  block  instruments  compels, 
under  ordinary  circumstances,  cyclic  operation  by  the  signalmen,  it  by 
no  means  follows  that  the  movements  of  all  classes  of  traffic  is,  or  can 
be,  made  in  one  unvarying  order.  Circumstances  are  constantly  arisin*g 
which  necessitate  deviation  from  the  simpler  routine  of  a  block  section, 
and  means  have  to  be  provided  to  meet  them.  These  are  obtained  by 
the  provision  of  a  "  releasing  key,"  by  the  use  of  which  certain  parts  of 
the  cycle  necessary  under  ordinary  conditions  may  be  anticipated  or 
dispensed  with.  The  importance  attached  to  the  use  of  the  release  key 
may  be  gauged  from  the  rules  relating  to  its  use  for  "cancelling," 
"  obstruction  danger,"  and  "  blocking  back "  signals,  failure  of  rail 
contact,  etc.,  and  the  special  caution  to  signalmen  "  not  to  resort  to  the 
key  until  they  are  quite  satisfied  that  its  use  is  really  necessary." 
Practically  speaking,  the  provision  of  the  releasing  key  is  an  acknow- 
ledgment of  the  want  of  sufficient  flexibility  to  meet  such  cases  as 
occur  in  the  common  operations  necessary  to  the  movement  of  traffic. 
As  such,  it  is  also  an  infraction  of  the  automatic  character  of  the 
system^  and  again  saddles  the  signalman  with  the  responsibility,  under 
the  ordinary  system,  of  which  it  is  the  object  of  the  lock  and  block  to 
relieve  him.  Granted  that  the  automatic  character  of  any  apparatus 
may  be  infringed  for  a  legitimate  purpose,  and  it  ceases  to  be  automatic. 
If  use  can  be  made  of  such  apparatus  under  conditions  that  are  suitable, 
there  is  nothing  to  prevent  its  use  under  misapprehension.  If  a  mis- 
apprehension exists  with  reference  to  the  conditions,  no  large-lettered 
cautions  will  prevent  its  use,  as  the  signalman  will  be  satisfied  of  its 
necessity,  and  recording  use  of  the  key  in  the  train-book  will  not  avert 
the  consequences  of  the  act.  Instances  have  occurred  where  use  of 
the  release  key  under  misapprehension  has  had  serious  results.  Hence, 
whilst  the  lock-and-block  is  undoubtedly  a  step  in  advance  of  the 
ordinary  system,  it  cannot  be  regarded  as  infallible,  since  in  the  use  of 
apparatus  provided  to  meet  certain  contingencies  the  signalman  must 
exercise  his  judgmem  as  to  whether  the  circumstances  absolutely 
warrant  the  course. 

The  type  of  rail  treadle  used  in  lock-and-block  systems  has  the 
grave  defect  that  it  will  clear  a  section  behind  it  when  under  certain 
circumstances  the  line  may  not  be  clear.  Such  treadles  are  actuated  to 
perform  the  release  operation  at  the  starting  signal  by  the  iirst  vehicle 
passing  over  them,  and  so  may  clear  a  section  by  the  first  portion  of  a 
train  which  has  become  divided.  Hence,  although  the  block  instru- 
ment would  be  released  by  the  first  portion  of  a  train,  and  may  again 
be  used  immediately,  yet  the  signalman  must  personally  assure  himself 
that  the  whpl?  tr^iQ  has  passed,  as  he  has  to  do  in  non-automatic 
systems. 


612  PIGG:    RAILWAY   BLOCK   SIGNALLING.      [Newcastle. 

In  connection  with  the  safety  of  snch  a  system,  we  have  with 
certain  classes  of  instruments  further  to  consider  the  effects  that  may 
be  produced  by  contact  between  the  block  wire  of  either  instrument 
and  another  working  wire,  and  of  the  effects  of  atmospheric  discharges. 
It  is  not  the  custom  to  build  separate  telegraph  lines  for  the  block 
circuits  any  more  than  it  is  not  the  custom  to  provide  a  separate  track 
for  each  train  operated.  Line  contacts,  no  doubt,  still  occur  occasionally, 
and  lightning  protectors  do  not  always  protect. 

Fog  Signalling,  etc. 

It  will  be  noted  that  the  lock  and  block  does  not  provide  checks  to 
obviate  the  consequences  of  neglect  or  inadvertence  on  the  part  of  one 
of  the  persons  concerned  in  the  movement  of  traffic — the  driver.  He 
is  left  altogether  out  of  consideration,  and  must  rely  upon  himself  for 
due  observance  of  the  signals  exhibited  for  his  guidance.  Yet  the 
driver  is  probably  the  most  important  of  the  persons  concerned,  since 
he  is  the  actual  controller  of  the  means  of  movement  of  traffic,  and 
is  the  last  link  in  the  chain  of  checks  imposed  by  signalling  systems. 
Whilst  accidents  have  taken  place  from  disregard  of  signals  in  clear 
weather,  the  duties  of  drivers  are  most  onerous  during  fogs  or  snow- 
storms, which  obscure  the  sight  of  the  signals  by  which  they  are  guided. 
Under  such  circumstances  the  visual  signals  are  supplemented  by 
explosive  signals  directly  operated  by  the  passage  of  trains  over  them. 
The  detonators,  which  are  placed  on  the  rails  in  the  neighbourhood  of 
the  signals  by  hand,  by  men  specially  collected  for  the  purpose  when 
such  signalling  becomes  necessary,  are  the  danger  signals,  but  they  are 
supplemented  by  signals  with  hand  lamps,  for  which  the  drivers  and 
firemen  must  watch.  The  signals  themselves  are  operated  by  the 
signalmen  in  the  usual  way,  and  the  fog-signalmen  act  in  accordance 
with  the  positions  of  the  signals  from  time  to  time.  Whilst  a  signal  is 
at  danger  the  detonators  must  remain  on  the  rails  ;  when  the  signal  is 
off  they  are  removed.  The  off  position  of  a  signal  which  cannot  be 
seen  is  therefore  indicated  to  a  driver  by  the  absence  of  an  explosion, 
and  the  hand-lamp  signals. 

Such  a  system  is  most  expensive  to  the  companies,  entails  consider- 
able exposure  and  hardship  upon  the  fog-signalmen,  and  suffers  from 
defects  of  a  practical  character  in  operation.  The  collection  of  the 
men  for  fog  signalling  occupies  some  time,  as  they  have  to  be  with- 
drawn from  other  duties,  or  to  be  brought  from  their  homes.  The 
person  who  has  to  decide  upon  the  necessity  or  otherwise  of  com- 
mencing fog  signalling  is  not  the  person  most  vitally  concerned,  or 
who  has  effective  control  of  the  movement  of  the  traffic  affected.  Fogs 
are  sometimes  of  a  deceptive  character,  and  appear  differently  to  a  man 
on  the  foot-plate  and  another  on  the  ground,  and  they  change  in 
intensity  very  rapidly  on  occasion.  The  "  All  right  "  signal  is  partly 
of  a  negative  character,  in  that  it  is  given  by  the  absence  of  explosion, 
together  with  the  hand-lamp  signals.  The  latter  signals  may  or  may 
not  be  seen  by  a  driver  or  fireman.  Sight  of  such  signals  involves 
either  continual  concentration  for  the  purpose,  or  the  ability  to  localise 
positions  so  as  to  be  able  to  look  specially  for  th^m  at  the  proper  time. 


1902.]  PIGG:    RAILWAY   BLOCK   SIGNALLING.  613 

This  question  of  localisation  of  position  is  of  some  importance. 
Experienced  drivers,  of  course,  know  the  "  feel "  of  the  road  perfectly 
well,  and  localise  their  position  from  a  large  number  of  local  circum- 
stances, such  as  the  passing  of  (over  and  under)  bridges,  curves, 
cuttings,  signals,  cabins,  stations,  etc.,  all  of  which  "talk"  to  them. 
Whilst  this  is  the  case  at  ordinary  speed  the  indications  are  not  so 
plain  at  lower  speeds,  and,  moreover,  approximately  the  same  indica- 
tions may  be  met  with  at  different  parts  of  a  journey.  Hence,  taking 
all  things  into  consideration,  the  present  system  of  fog  signalling  leaves 
something  to  be  desired. 

Attempts  have  been  made  to  place  the  operation  of  the  fog  signals 
in  the  hands  of  the  signalmen,  but  whilst  such  methods  enable  the 
system  to  be  brought  into  use  more  promptly  than  when  hand  signal- 
ling is  resorted  to,  and  obviate  hardship  and  exposure  to  the  fogmen, 
it  does  not  alter  the  character  of  the  signal,  and,  moreover,  it  does  not 
allow  of  personal  supervision,  and  abolishes  the  supplementary  hand 
signals.  Probably  the  most  promising  systems  for  superseding  the 
ordinary  fog  signalling  are  those  which  provide  for  the  signal  being 
given  directly  upon  the  engine  itself,  and  for  it  to  be  in  constant 
operation.  There  is  quite  a  large  number  of  such  systems  available 
now,  but  taking  the  whole  country  into  consideration  their  adoption  is 
not  proceeding  at  a  great  rate.  Some  of  the  systems  referred  to  are 
mechanical,  such  as  that  devised  by  Mr.  Raven,  of  the  North- Eastern 
Railway,  and  which  is  being  fitted  to  a  large  number  of  the  company's 
engines ;  others  are  partly  mechanical  and  partly  electrical,  as  Mr. 
Brierle/s  system,  which  has  been  introduced  by  Messrs.  Saxby  and 
Farmer;  others  again  are  wholly  electrical,  such  as  the  method  of 
signalling  devised  by  Lieutenant-Colonel  Bolitho.  The  majority  of 
such  systems  operate  by  means  of  an  obstruction  working  in  conjunc- 
tion with  the  signal  to  be  indicated,  placed  on  the  line,  which  gives  an 
alarm  on  the  engine,  and  so  calls  attention  to  the  position  of  the  signal. 
In  Mr.  Raven's  system  the  alarm  is  a  special  whistle  which  may  be 
operated  by  steam  or  compressed  air.  In  Mr.  Brierley's  and  Lieutenant- 
Colonel  Bolitho's  systems  attention  is  drawn  by  means  of  electric  bells 
and  discs,  and  electric  bells,  respectively,  carried  on  the  engine.  In 
the  latter  the  electrical  circuits  are  closed  by  contact  with  steel  brushes 
placed  on  the  line  side  in  a  similar  way  to  that  previously  used  by  Mr. 
Burns  and  others.  In  some  of  the  systems  an  alarm  when  the  signal  is 
'*  on  *'  is  considered  sufficient ;  in  others,  again,  provision  is  made  for 
repeating  both  the  "on"  and  "off"  positions,  so  that  the  signal  is 
positive  in  both  cases. 

It  is,  of  course,  impossible  to  enter  into  a  detailed  description  of 
such  systems,  or  even  to  enumerate  all  of  them.  Mention,  however, 
should  be  made  of  the  system  devised  by  Mr.  W.  S.  Boult,  in  which 
necessity  for  contact  between  parts  of  moving  vehicles  and  obstructions 
on  the  line  is  obviated.  This  is  done  by  the  use  of  permanent  and 
electro  magnets  placed  on  the  line,  the  latter  being  operated  in  con- 
junction with  the  signals.  The  magnets  act  upon  polarised  relays 
carried  upon  the  engine  in  such  positions  as  to  pass  immediately  over 
the  former,  and  the  relays  operate  appropriate  circuits  for  the  purposes 


614  PIGG:    RAILWAY   BLOCK   SIGNALLING.      [Newcastle. 

required  on  the  engine.  The  indications  given  on  the  engine  are  visual 
(miniature  distant  and  stop  signals,  and  numbered  and  coloured  discs) 
and  aural  (bells).  The  system  distinguishes  between  "  on  "  and  "  off/' 
between  "distant"  and  "stop"  signals,  provides  route  indicators  to 
show  on  the  engine  which  road  has  been  prepared  at  junctions,  is 
capable  of  repeating  the  signals  in  the  cabins,  and  is  self-testing  for 
both  engine  and  line  circuits.  Failure  of  the  line  or  engine  circuits 
also  results  in  the  danger  signal  being  given  at  the  next  signal 
approached  after  the  failure,  and  partial  failure  of  the  latter  circuits 
is  distinguishable.  One  special  feature  of  the  system  lies  in  the  fact 
that  the  last  indication  received  on  the  engine  remains  until  the  next 
signal  is  reached,  and  so  serves  as  a  continual  reminder  of  the  condi- 
tions under  which  the  train  is  running.  This  result  is  not  obtained 
with  the  present  system  of  visual  signalling,  and  its  value  in  a  case 
where  a  driver  has  failed  to  comply  with  the  signals  exhibited  is 
obvious,  whilst  the  ability  to  distinguish  between  distant  and  stop 
signals  is  a  valuable  characteristic  for  purposes  of  localisation.  The 
indications  given  upon  the  engine  are  of  the  most  positive  character, 
the  semaphore  arms  being  first  thrown  to  "  danger,"  after  which  they 
either  remain  in  that  position  if  the  actual  signal  is  "on,"  or  are 
immediately  lowered  if  the  signal  is  "off."  The  system  is  of  the 
most  complete  character,  and  its  design  shows  the  closest  study  of  the 
conditions  to  be  met,  whilst  the  details  of  the  apparatus  are  most 
ingenious  and  at  the  same  time  very  simple.  Its  adoption  would 
revolutionise  the  method  of  signalling,  since  practically  there  would  be 
no  necessity  for  providing  the  mechanical  signals  now  in  use. 

The  selection  of  a  system  of  auxiliary  signalling  such  as  has  been 
considered  has  a  business  aspect,  as  well  as  the  technical  and 
operative  sides.  In  order  to  get  the  utmost  value  from  such  a 
system,  it  should,  since  engines  run  over  other  companies*  lines  than 
their  own,  be  uniform  for  all  lines  if  possible,  or  at  least  for  the 
lines  over  which  interchange  of  locomotives  takes  place.  Some  com- 
panies might  be  able  and  willing  to  pay  more  for  the  additional 
security  to  be  obtained  than  others ;  and  some,  again,  might  consider 
certain  precautions  essential  which  to  others  might  appear  to  be 
superfluous,  or  not  worth  the  cost  of  obtaining.  The  matter  is  one 
for  common  agreement  amongst  the  companies  running  over  each 
other's  lines.  Otherwise,  the  subject  is  likely  to  prove  a  worthy 
successor  to  the  position  so  long  held  by  proposals  to  supersede  the 
cord  communication  by  electrical  means — a  matter  for  wordy  debate 
to  be  settled  eventually  by  the  adoption  of  other  means. 

"  Automatic  "  Signalling. 
Summing  up  the  situation  as  it  appeared  to  him  in  1898,  the  present 
speaker  wrote :  "  Railway  signalling  appears  to  have  now  reached  a 
stage  at  which  some  departure  from  the  present  methods  seems 
probable.  The  lines  upon  which  changes  will  be  made  will,  in  all 
probability,  result  in  a  greater  degree  of  automatic  control  than 
obtains  at  present."  The  indications  at  present  seem  to  confirm  this 
view  very  strongly,  and  we  appear  to  be  likely  to  see  early  changes  in 


1902.]  PIGG:    RAILWAY  BLOCK  SIGNALLING.  615 

the  methods  of  signalling  of  the  most  radical  character.  The  American 
"  track  circuit "  system  is  gaining  a  footing  in  this  country,  and  if  it 
should  be  found  suitable  for  a  country  where  junctions  are  so  numerous 
and  near  together,  and  where  the  great  bulk  of  traffic  is  between  points 
comparatively  near  to  each  other,  a  revolution  will  be  effected  which 
will  at  once  change  the  whole  character  of  signalling  in  this  country. 
And  there  is  no  more  reason  to  doubt  that  the  success  of  such  a  system 
will  result  in  financial  relief  to  the  companies  than  there  is  to  doubt  the 
necessity  for  such  relief. 

In  this  country  there  is  already  an  installation  of  automatic  signal- 
ling in  operation  between  Grateley  and  Andover,  on  the  London  and 
South-Western  Railway,  in  which  the  signals  are  actuated  by  air  on 
the  low-pressure  system,  the  movements  being  controlled  by  the 
positions  of  trains  on  the  line,  which  is  formed  into  track  circuits. 
The  North-Eastern  Railway  Company  has  also  made  arrangements 
with  the  Hall  Signal  Company  of  America  to  equip  a  portion  of  their 
main  line  to  the  North,  between  Alne  and  Thirsk,  with  a  track  circuit 
system  of  automatic  operation.  This  installation  will  differ  from  the 
ordinary  Hall  system — in  which  the  signals  are  operated  by  electric 
motors — and  from  the  London  and  South-Western  Company's  installa- 
tion, in  that  the  signals  will  be  self-contained  as  regards  motive  power. 
Movements  Will  be  made  by  carbonic  acid  contained  in  steel  cylinders 
at  a  pressure  of  600  lb.  per  square  inch,  the  working  pressure  being 
50  lb.  As  many  as  10,000  movements  can  be  obtained  before  it 
becomes  necessary  to  recharge.  At  the  junctions  between  Alne  and 
Thirsk  the  automatic  signals  leading  to  fouling  points  with  the  branch 
lines  will  also  be  under  manual  control,  so  as  to  admit  of  branch 
working.  Such  cabins,  however,  will  be  closed  at  times  when  the 
branch  traffic  ceases.  The  sections  will  be  shorter  than  ordinary. 
Siding  points  connecting  with  the  main  line  in  the  purely  automatic 
sections  will  be  provided  with  indicators  communicating  with  several 
of  the  rear  sections  to  show  whether  trains  are  approaching  before  the 
switches  are  opened  for  the  siding.  It  is  expected  that  a  considerable 
annual  saving  in  the  working  expenses  for  the  signalling  of  that  portion 
of  the  line  will  result  from  the  change,  and  if  this  is  effected  and  the 
system  is  otherwise  satisfactory,  no  doubt  further  extensions  will  follow 
in  the  near  future. 

Taken  on  the  whole,  railway  signalling  in  the  States  is  of  a  very 
mixed  character,  and  varies  from  the  antiquated  "train  dispatcher" 
system,  with  or  without  telegraphic  communication,  through  the  tele- 
graphic, the  manually  operated,  manually  controlled,  and  the  con- 
trolled manual,  to  the  automatic  systems.  There  is  not  time  here  to 
discuss  these  systems,  or  the  many  other  interesting  details  of  American 
signalling,  such  as,  for  instance,  the  relative  advantages  of  the  "  normal 
clear  "  or  "  normal  danger  '*  positions  for  signals ;  two  or  three  p)osition 
signalling ;  track  sections  versus  treadles  for  the  controlled  manual ; 
the  simple  single  signal,  the  overlap,  or  the  home  and  distant  systems ; 
the  operation  of  signals  by  electricity  or  air,  and  high  or  low  pressure 
for  the  latter ;  track  batteries  and  relays ;  the  bonding  and  insulating 
of  rails ;  and  other  matters  of  a  very  practical  character.  The  auto- 
VOL.  82.  41 


616  PIGG:    RAILWAY    BLOCK   SIGNALLING.      fNewcasUc, 

matic  system  seems  to  have  taken  firm  hold,  and  when  we  consider  its 
advantages  as  looked  at  in  the  States,  there  seems  to  be  little  cause  for 
wonder  that  it  has  done  so,  especially  in  a  country  where  long  con- 
tinuous runs  between  diverging  points  are  common.  The  reasoning 
adopted  is  very  plain,  as  the  following  quotations  from  a  series  of 
articles  in  the  Electrical  Review  last  year  will  show :  "  If  the  substitu- 
tion of  automatic  devices  for  the  control  of  a  system  formerly  under 
human  control  and  operation  (the  controlled  manual  is  being  referred 
to)  produced  such  beneficial  results,  why,  one  naturally  asks,  should 
not  the  introduction  of  automatic  mechanisms  for  its  operation  pro- 
duce like  benefits."  "  It " — the  automatic  system — "  is  constantly  on 
duty,  requires  no  relief  substitute,  never  goes  on  strike  nor  tires  of  its 
job,  never  sleeps,  gets  drunk,  or  deserts  its  pals,  and  never  misconstrues 
orders."  "  The  ideal  system  is  one  in  which  the  train  in  a  block  has 
control  of  the  signals  governing  the  entrance  to  that  block."  "The 
system  affords  means  of  detecting  misplaced  switches  in  the  block,  of 
failure  of  cars  on  a  side  track  to  stand  clear  of  the  running  line,  has 
frequently  detected  broken  rails  and  obstructions  in  switches,  it  affords 
opportunity  for  trackmen  to  protect  blocks  during  emergencies,  and 
for  protection  during  repairs."  "Operators  for  such  a  system  are 
superfluous,  and  could  only  be  of  use  in  case  of  derangement."  "  Rail- 
road officials  are  universally  awakening  to  the  possibilities  of  automatic 
signals,  and  that  wages  are  better  utilised  in  obtaining  automatic 
operation." 

Another  advantage  claimed  for  the  automatic  system  is  that  the 
carrying  capacity  of  a  line  may  be  increased  from  the  facility  with 
which  the  block  sections  may  be  shortened.  On  this  subject,  how- 
ever, the  last  word  is  not  with  the  signalling  systems,  since  the  lengths 
of  the  sections  must  always  be  such  as  to  allow  any  train,  whatever  its 
speed,  weight,  and  braking  power,  to  be  brought  to  a  stand  in  the  space 
allotted.  The  suggestion,  moreover,  involves  a  levelling  of  speeds^ 
which  again  will  require  limitation  of  loads  for  mixed  traffic,  since 
the  standard  of  speed  will  always  be  set  by  the  fast  passenger  .traffic. 
There  is  no  tendency  ascertainable  in  either  of  these  directions  at 
present. 

Further  study  of  automatic  systems  shows  the  great  necessity  for 
supplementary  signalling  under  exceptional  circumstances,  such  as 
fog  or  snow,  since  there  is  no  personal  supervision.  Some  form  of 
apparatus  giving  the  signals  on  the  engine  would  seem  to  be 
imperative. 

Where  automatic  signals  are  in  use,  the  rule  that  a  stop  signal  shall 
not  be  passed  when  in  the  danger  position  unless  other  signals  are 
given  which  are  recognised  as  superseding  it,  must  necessarily  be 
abolished,  and  a  time  limit  of  detention  at  the  signal  imposed,  after 
observance  of  which  the  train  goes  cautiously  forward  until  ordinary 
signalling  is  resumed  in  the  sections  ahead.  Unless  special  regulations 
or  provisions  are  made,  and  in  the  event  of  prolonged  operations  at  a 
point  giving  access  to  the  main  line,  this  may  result  in  a  train  arriving 
at  the  signal  actually  protecting  a  train  drawing  on  to  the  main  line^ 
when,  of  course,  the  space  limit  will  not  be  observed. 


1902.]  PIGG:    RAILWAY  BLOCK   SIGNALLING.  617 

In  the  States,  it  is  usual  to  distinguish  signals  which  may  be  passed 
at  "danger"  after  a  time  interval  from  those  which,  being  under 
manual  control,  may  not  be  passed  without  special  instructions. 
Where  signals  are  at  one  period  automatic  and  at  another  under 
manual  control,  the  conditions  are  more  complex. 

Possibilities  of  Signalling   with    Electric  Traction. 

We  have  seen  that  the  adoption  of  human  control  for  railway 
signalling  has  necessitated  the  imposition  of  numerous  checks  upon 
the  actions  of  the  controllers,  and  has  required  considerable  auxiliary 
apparatus  for  a  variety  of  purposes.  The  adoption  of  automatic 
signals  dispenses  with  all  the  costly  apparatus  referred  to,  except  at 
junctions  where,  owing  to  the  want  of  selective  properties,  automatic 
systems  are  unsuitable.  The  question  for  consideration  now  is,  "  Is 
the  automatic  system,  as  described,  final  ? "  If  we  consider  the  present 
outlook  with  regard  to  railways,  we  find  that  we  are  probably  on 
the  eve  of  a  very  great  change  in  methods  and  even  routine  of 
transportation.  The  great  question  to  be  now  decided  concerns  the 
use  of  the  self-dependent  locomotive,  or,  as  an  alternative,  the  use  of 
locomotives  taking  their  power  from  their  locality,  wherever  that 
may  be,  in  the  line  of  their  run.  The  question  is  not  entirely  confined 
to  steam  and  electricity,  although  at  present  these  two  are  the  only 
ones  worth  considering.  As  all  are  aware,  the  railway  companies  are 
taking  action  in  consequence  of  the  incursion  of  the  electric  tram  into 
what  has  hitherto  been  practically  a  monopoly.  The  directors  of  the 
North-Eastern  Railway  are  considering  tenders  for  the  equipment 
of  part  of  their  lines  in  this  neighbourhood  for  the  use  of  electric 
power;  the  Lancashire  and  Yorkshire  have  partly  completed  their 
arrangements ;  the  London  and  North- Western  are  said  to  be 
considering  the  question  ;  and  the  Great  Eastern  are  to  apply  for 
powers  for  the  same  purpose  as  early  as  possible.  The  proposals  now 
being  put  forward  are  for  comparatively  short-distance  suburban 
traffic ;  the  electrification  of  long-journey  main  lines  is  not  just 
yet. 

The  point  for  consideration  here,  however,  is  not  the  suitabilitv  or 
otherwise  of  electric  traction,  but  the  effects  that  it  may  have  on 
signalling.  If  we  look  over  the  principal  equipments  of  a  train,  we 
find  that  we  have  steam  for  locomotion;  gas,  oil,  or  electricity  for 
lighting ;  and  pneumatic  appliances  for  braking.  Electricity  is 
capable  of  displacing  all  these  for  each  of  their  several  purposes.  As 
electrical  power  is  delivered  to  the  locomotives  from  the  outside,  we 
have  presented  to  us  conditions  which  have  no  precedent,  and  oppor- 
tunities for  outside  control  such  as  have  never  before  existed.  Hitherto 
the  driver  has  been  the  sole  actual  controller  of  the  means  of  loco- 
motion, and  short  of  throwing  the  train  off  the  line,  or  into  a  dead  end, 
no  other  person  could  affect  the  results  when  he  neglected  certain 
duties.  With  electricity  all  this  is  altered,  and  we  have  to  deal  with 
an  agent  which  is  easily  handled,  and  lends  itself  readily  to  automatic 
or  other  control  and  operation.  American  automatic  signalling  gives 
contro}  9(  the  signals  to  the  train  requiring  their  protection.    Where 


618  PIGG:    RAILWAY  BLOCK  SIGNALLING.      [NewcasUc, 

supplementary  signalling  is  in  use  to  check  error  on  the  part  of  the 
driver,  its  design  is  generally  with  a  view  to  direct  action  on  the 
control  of  the  motive  power,  rather  than  to  call  attention  to  a  derelic- 
tion of  duty,  as  with  us.  With  electric  traction  there  should  be  no 
difficulty  in  arranging  to  give  such  direct  control  to  the  train  which 
requires  to  be  protected  by  cutting  off  the  power  from  all  sections  that 
would  endanger  its  course,  whether  these  are  "following,"  "con- 
verging," or  "crossing."  Signals  as  now  used  would  then  be  super- 
fluous, except  at  such  places  as  those  where  selection  of  traffic 
rendered  them  necessary.  Control  of  the  motive  power  is  a  far  more 
effective  check  on  inadvertence  than  any  other  that  can  be  devised. 
The  whole  aim  of  the  signalling  now  in  use  on  railways  is  to  control 
the  man  who  controls  the  motive  power.  If  we  can  give  to  a  train  the 
means  of  controlling  the  motive  power  to  other  trains,  which  may  be 
sources  of  danger  to  it,  the  men  who  control  the  motive  power  on  those 
trains  will  no  longer  count  in  connection  with  the  subject  under  notice. 
After  all,  automatic  signalling,  as  described,  does  no  more  for  the 
driver  than  the  manual  or  the  controlled  manual,  if  as  much,  since  it 
removes  the  personal  supervision  now  provided,  which  is  not  always 
faulty,  and  has  on  many  occasions  been  of  the  highest  possible 
value. 

The  author's  thanks  are  due  to  Mr.  Raven,  of  the  locomotive  depart- 
ment, and  Mr.  Ellison,  the  superintendent  of  the  telegraph  department 
of  the  North-Eastern  Railway,  and  to  Mr.  Fletcher  of  the  L.  and  N.W. 
Railway,  for  the  loan  of  apparatus  for  use  at  the  meeting. 

Mr 

Hciiviside.  Mr.  A.  W.  Heaviside  said  that,  with  regard  to  Mr.  Pigg's  paper  on 

"  Railway  Block  Signalling,"  they  were  certainly  obliged  for  such  an 
exhaustive  statement  of  what  is  done  in  this  direction  at  the  present 
time,  which  is  a  very  critical  one  in  the  history  of  block  signalling. 
He  was  one  of  a  party  which  recently  visited  Tyne  Dock  to  see  the 
system  in  operation  there,  and  it  occurred  to  him  that  the  capital  cost 
was  very  considerable— rather  more  than  the  ordinary  system.  He  did 
not  see  why  they  should  not  do  the  whole  thing  electrically,  and  not 
use  pneumatic  power  at  all.  If  a  man  were  to  commence  to  build  a 
new  railway  at  the  present  time,  he  did  not  think  it  likely  that  he  would 
proceed  on  the  same  methods  as  the  existing  arrangements.  The  old 
system  requires  a  great  deal  of  maintenance.  Mr.  Pigg  had  said  that 
the  North-Eastern  Railway  Company  had  employed  the  telegraph  and 
the  telephone  as  an  auxiliary,  and  he  would  be  very  glad  to  hear  more 
about  his  experiences  with  the  telephone.  There  were  many  other 
interesting  questions  which  might  be  raised,  but  in  the  absence  of  Mr. 
Pigg  it  was  rather  difficult  to  carry  the  discussion  much  further. 

Mr.  Moir.  Mr.   A.   MoiR   said  that,  while  asking  for    more    seemed  rather 

ungracious,  seeing  the  paper  was  so  long  and  exhaustive,  if  Mr.  Pigg 
had  been  there  he  would  have  liked  to  have  asked  him  what  the 
resistance  of  the  block  coils  is  which  they  use  on  the  North-Eastern 
Railway,  how  many  amperes  were  required  to  actuate  the  instru- 
ments, what  sort  of  primary  battery  did  they  find  gave  best  results ; 
also  whether  secondary  cells  have  been  employed  with  any  success 


1902.]         RAILWAY  BLOCK  SIGNALLING:    DISCUSSION.  619 

Mr.  R.  M.  Longman  :  With  reference  to  Mr.  Pigg's  statement  that  Mn 
no  passengers  lost  their  lives  in  190 1,  it  may  be  added  that  many  fatal 
accidents  occurred  at  highway  level  crossings,  due  in  many  cases  to 
carelessness  or  forgetfulness  on  the  part  of  the  gatemen,  who  often 
open  their  gates  without  placing  their  signals  against  the  trains.  A 
little  interlocking  device  would  thus  save  many  lives. 

Mr.  J.  PiGG  (in  reply,  communicated) :  I  regret  that  a  misunderstanding  Mr.  Pigg. 
and  my  recovery  from  an  illness  led  to  my  absence  from  the  meeting 
of  January  19th  and  have  further  prevented  a  full  discussion  of  the 
problems  to  be  met  with  in  railway  signalling.  There  can  be  little 
doubt,  as  remarked  by  Mr.  Heaviside,  that  the  capital  expenditure  for 
such  a  system  as  he  inspected  is  greater  than  that  for  the  ordinary 
system ;  but  if  a  commensurate  saving  is  effected,  either  in  labour  or 
by  facilitating  the  operation  of  traffic,  the  increased  expenditure  will  be 
justified.  Whether  such  a  saving  will  be  shown  remains  to  be  seen. 
The  period  of  use  is  at  present  too  short  to  enable  a  reliable  opinion  to 
be  formed.  It  must,  moreover,  be  remembered  that  the  maximum 
economy  is  not  to  be  expected  from  such  a  system  in  small  isolated 
installations  with  separate  equipments  for  motive  power. 

The  employment  of  the  telegraph  and  telephone  in  connection  with 
the  operation  of  railway  traffic  is,  as  stated,  auxiliary  to  the  ordinary 
block  signalling,  and  does  not  differ  materially  from  the  methods  of 
using  such  instruments  elsewhere.  They  are  not  used  directly  in  block 
signalling,  but  for  perfecting  arrangements  before  traffic  is  allowed  on 
the  line,  or  for  giving  information  beyond  the  scope  of  the  code,  or  for 
communication  between  block  points  not  directly  connected  for  sig- 
nalling purposes.  The  telegraph  is  used  for  transmitting  notice  of  the 
times  trains  leave  or  pass  certain  points  to  other  places  on  their  routes, 
so  that  proper  arrangements  can  be  made  for  dealing  with  them  without 
unnecessary  delay  to  other  traffic.  The  telephone  is  used  for  similar 
purposes,  but  more  locally  and  over  less  extended  distances  ;  although 
valuable  auxiliaries  for  the  working  of  traffic,  they  are  not,  of  course, 
part  of  the  block  system  proper. 

With  reference  to  Mr.  Moir's  questions,  the  block  indicators  in  use 
on  the  North- Eastern  Railway  are  wound  to  a  resistance  of  about 
150  ohms.  The  batteries  used  are  the  ordinary  porous-pot  Leclanche 
cells.  A  six-cell  battery  is  used  for  the  pinning  instruments,  and  a 
four-cell  set  for  the  non-pinning.  (Since  the  reading  of  the  paper  the 
North-Eastern  Railway  has  ceased  to  use  the  block  indicators  in  con- 
nection with  the  code,  and  no  doubt  the  non-pin  batteries  will  be 
dispensed  with.)  I  have  no  idea  of  the  minimum  current  required  by 
the  block  indicators.  On  the  North-Eastern  Railway  they  work  perfectly 
well  with  ten  milliamperes,  but  they  are  never  intentionally  worked  with 
the  minimum. 

Secondary  cells  have  not,  to  the  writer's  knowledge,  been  tried 
anywhere  for  block  working,  and  the  prospect  of  their  adoption  does 
not  seem  very  great.  The  first  cost  and  maintenance  of  such  cells 
would  seem  to  be  necessarily  greater  than  that  of  primary  cells,  and 
the  amount  of  apparatus  in  the  average  signal  cabin  hardly  calls  for  the 
adoption  of  the  universal  battery  system  which  the  use  of  storage  cells 


620  PIGG:    RAILWAY  BLOCK  SIGNALLING.      [Newcastle, 

Mr.  Pigg.  SO  greatly  facilitates.  Moreover,  such  a  battery  arrangement  is  for 
railway  signalling  an  operation  of  the  nature  of  putting  too  many  eggs 
in  one  basket.  It  is  desirable  that  the  signalling  of  the  different  lines 
should  be  as  independent  as  the  lines  themselves  are  for  the  operation 
of  traffic. 

There  is  a  certain  amount  of  truth  in  Mr.  Longman's  remarks 
respecting  accidents  at  gate  crossings.  Accidents  do  occasionally 
occur  at  such  places,  but  although  the  writer  has  mixed  intimately  with 
gatemen  over  a  considerable  area  of  this  country,  and  although  he  pays 
great  attention  to  the  reports  of  the  inspectors  of  the  Board  of  Trade, 
he  would  not  go  so  far  as  to  say  that  they  often  open  their  gates  without 
placing  their  signals  against  the  trains.  There  are  many  cases  in  the 
writer's  own  knowledge  where  signal  cabins  are  erected  at  highway 
crossings  solely  on  account  of  the  traffic  on  the  road.  In  these  and  in 
all  cases  where  the  gates  and  signals  are  worked  from  one  point  the 
gate- wheel  is  interlocked  with  the  signal  levers.  In  others  cases  a 
dwarf  frame  is  provided  which  affords  the  interlocking  referred  to. 
At  gate  crossings  between  block  points  many  companies  provide 
electrical  apparatus,  connected  in  the  block  circuits  passing  the  gates, 
by  which  the  gateman  is  constantly  aware  of  the  condition  of  the  line 
on  both  sides  of  his  gates. 


1903.]  CHArrOCK;   MOTIVE   POWER  SUPPLY.  621 

LEEDS  LOCAL   SECTION. 


MOTIVE   POWER   SUPPLY   FROM   CENTRAL 
STATIONS. 

By   R.  A.  Chattock,   Member. 

{Paper  read  at  Meeting  of  Section^  February  igth^  ^90J.) 

The  development  of  a  supply  of  electric  energy  for  motive  power  to 
private  consumers  has  been  occupying  the  attention  of  Central  Station 
Engineers  for  a  considerable  time,  and,  during  the  last  two  or  three 
years,  has  been  stimulated  very  much  by  the  excellent  results  that  have 
been  obtained  in  several  large  towns.  It  is  obvious  that,  given  a  large 
network  of  mains  that  has  been  laid  for  the  purpose  of  supplying  light- 
ing consumers,  it  is  to  the  interest  of  these  consumers,  as  well  as  of  the 
authority  responsible  for  the  supply,  to  have  as  much  current  as 
possible  distributed  through  it,  especially  during  the  hours  of  daylight. 
The  lighting  consumer  benefits  by  the  greater  output  combined  with 
the  increased  load-factor  at  the  generating  station,  making  it  possible 
to  generate  current  at  a  cheaper  rate.  The  supply  authority  benefits 
by  being  able  to  reduce  the  cost  of  supply  and  by  having  the  demand 
for  current  stimulated.  The  standing  charges  on  the  cost  of  the  mains 
are  spread  over  a  greater  output  and  so  reduced  proportionately. 

Direct-current  stations,  so  far,  have  done  most  in  developing  this 
branch  of  the  supply.  This  is  probably  because  the  direct-current 
motor  has,  up  to  recent  times,  been  more  easily  applied  to  existing  con- 
ditions, and  has  proved  a  more  reliable  and  efficient  machine  than  the 
single-phase  alternating-current  motor.  Now  that  alternating-current 
stations  are  changing  over  to,  or  putting  down,  auxiliary,  two-  and 
three-phase  plant,  this  disadvantage  should  disappear,  and  the  engineer 
in  charge  of  such  a  station  should  be  able  to  follow  in  the  steps  of  his 
direct-current  brother. 

It  may  be  interesting  to  give  a  short  description  of  what  has  been 
done  in  connection  with  a  supply  of  current,  for  motive  power,  by  the 
Corporation  of  the  City  of  Bradford.  The  supply  is  by  means  of  direct- 
current,  the  voltage  being  230  or  460.  The  first  motor  was  connected 
to  the  mains  in  1891.  There  was  not  much  development  until  1897, 
when  the  Corporation  inaugurated  a  system  of  hiring  out  motors,  and  at 
the  same  time  reduced  the  price  for  current  to  2id.  per  unit.  In  1896 
the  percentage  of  current  sold  for  motive  power  to  the  total  output  was 
only  67  per  cent.  This  percentage  has  rapidly  increased  as  the  facilities 
provided  for  obtaining  motors  have  been  realised  and  appreciated  by 
the  public,  and  as  the  charge  for  current  has  been  reduced  to  the 
existing  rates  of  2d.  for  intermittent  use,  and  id.  for  continuous  use, 
until,  in  1902,  it  stood  at  49'25  per  cent. 

The  gradual  increase  in  this  branch  of  the  supply  is  set  forth  in  the 
following  table,  which  also  shows  the  improved  load-factor  of  the 
generating  station. 


622 


CHATTOCK:  MOTIVE   POWER  SUPPLY 


[Leeds, 


Year. 


I 


1893. 


Molors  on  the  Supply,  Dec.  31st.  On  Hire 
Motors  on  the  Supply,  Dec.  31st.     Not  on 

Hire   , 

Motors  on  the  Supply,  Dec.  31st.    B.H.P. ... 

Units  sold  for  Motive  Power    

Total  Units  sold  to  Private  Consumers 

Percentage  of  Motor  Units  on  Total  Units... 
Price  charged  per  Unit  for  Motive  Power... 
Average  Price  per  Unit  obtained  for  Motive 

Power    

Load  Factor,  excluding  Traction,  per  cent. 


26 
110 

480,494 
402 
4id. 

4-5d. 
313 


1896. 


58 
244 

54.972 

8x3,623 

676 

3id. 

3-5d. 
8-93 


525 

229 
3460 
1,297,120 
3,012,158 

4306 
2d.  &  Id. 

i-20d. 
1174 


1902.* 


641 

272 

4,398 

1,899,873 

3,857,757 

4925 
2d.  &  Id. 

I-I7d. 
1378 


*  The  figures  for  1902  are  approximately  correct. 


During  these  years  it  has  been  possible  to  reduce  the  charge  per 
unit  for  current  supplied  to  the  lighting  consumers  from  6d.,  in  1892,  to 
4Jd.,  less  2^  per  cent,  discount  and  a  free  supply  of  incandescent  lamps, 
in  1899.  The  price  has  stood  at  this  figure  up  to  the  present  date,  but 
the  Corporation  anticipate  that  they  will  be  able  to  reduce  it  still  further 
in  the  near  future. 

In  calculating  the  cost  of  generation  of  a  motive  power  supply,  when 
this  is  combined  with  a  lighting  supply,  the  following  points  must  be 
borne  in  mind : — It  is  not  necessary  to  increase  the  staff  of  men 
employed  in  the  station  beyond  what  would  be  required  for  a  pure 
lighting  supply.  The  management  expenses,  rents,  rates,  and  taxes 
remain  the  same.  The  plant  installed  in  the  generating  station  has  to 
be  increased  only  very  slightly,  owing  to  the  fact  that  the  main  part  of 
the  motive  power  supply  is  discontinued  at  5  p.m.,  before  the  peak  of 
the  lighting  load  has  to  be  met ;  the  part  that  does  overlap,  can  be  safely 
and  most  economically  dealt  with,  by  slightly  overloading  the  station 
plant,  for  half  an  hour  a  day,  for  about  six  weeks  during  the  twelve 
months.  The  question  of  black  fogs,  of  a  density  sufficient  to  necessi- 
tate a  supply  during  the  hours  of  daylight,  equal  to  the  maximum 
lighting  load,  has  very.rarely  to  be  considered,  so  rarely  that  it  really  only 
affects  one  or  two  towns  in  the  country.  A  fog  such  as  is  ordinarily  met 
with  will  not  create  a  demand  for  more  than  75  per  cent,  of  the  maxi- 
mum lighting  load,  and  it  is  found  in  practice  that  the  motive  power 
supply  can  be  satisfactorily  dealt  with  by  the  plant  installed. 

The  same  considerations  apply  to  the  question  of  extending  the 
distributing  network  of  mains.  It  is  found  that  the  majority  of  motors 
installed,  are  connected  to  the  existing  network,  which  has  been  laid 
for  the  supply  of  lighting  consumers,  and  the  current  used  by  these 
motors  helps  to  utilise  the  mains  during  the  hours  of  daylight.  This  is 
a  set-off  against  any  small  extensions  that  it  may  be  necessary  to 
make  to  supply  outlying  power  consumers.  In  some  cases,  however, 
considerable  extensions  may  be  necessary ;  these  should  be  considered 
separately,  and  if  the  estimated  revenue  from  the  current  supplied  does 


1903.]  FROM   CENTRAL   STATIONS.  623 

not  equal  a  certain  percentage  on  the  cost  of  the  extension,  the  applica- 
tion should  not  be  entertained,  unless,  of  course,  the  applicant  is  will- 
ing to  pay  such  a  sum  towards  the  cost  of  the  extension,  as  will  make 
it  remunerative. 

The  minimum  percentage  on  the  cost  of  an  extension,  that  it  is  policy 
to  require,  must  be  difiFerent  in  different  towns,  and  can  only  be  ascer- 
tained by  experience.  As  a  basis  to  go  upon,  a  percentage  of  lo  per 
cent,  is  suggested,  this  figure  having  worked  out  satisfactorily  as  regards 
the  City  of  Bradford. 

It  may  be  safely  assumed,  therefore,  that  the  cost  of  generation 
should  not  be  estimated  to  include  the  following  items  : — 

Wages  in  Generating  Station. 
Management,  rents,  rates,  and  taxes. 

Standing  charges  upon  the  outlay  in  respect  of  station  plant 
and  distributing  mains. 

The  items  which  should  be  included  are  as  follows,  and  these  should 
be  taken  at  the  full  rate  per  unit  for  the  whole  of  the  supply  : — 

CoaL 

Water. 

Oil,  stores,  etc. 

Repairs  and  maintenance  of  plant  and  mains. 

Turning  now  to  the  considerations  affecting  the  price  to  be  charged. 
It  has,  during  the  last  four  years,  been  the  practice  in  Bradford  to 
charge  one  penny  per  unit  for  motors  used  continuously  throughout  the 
working  hours  of  the  day,  and  twopence  per  unit  for  those  used  inter- 
mittently. This  method  of  charging  has  answered  fairly  well,  though 
it  is  open  to  several  objections.  For  instance,  some  power  customers 
who  use  their  motors  intermittently  consume  a  much  greater  number 
of  units  per  horse-power  installed  than  others  who  have  motors  running 
continuously  ;  again,  it  is  often  very  difficult  to  decide  whether  the  use 
of  a  motor  is  intermittent  or  continuous. 

The  maximum  demand  system  of  charging  is  not  so  applicable  to 
motor  supply  as  it  is  to  lighting  supply,  on  account  of  the  fluctuating 
nature  of  the  load  on  a  motor,  and  of  the  liability  to  sudden  heavy  over- 
loads. The  effect  of  these  overloads  is  not  necessarily  felt  by  the  gene- 
rating station  at  the  peak  load  time,  but  the  reverse  of  this  is  rather  the 
case. 

It  would  seem  that  the  best  method  of  charging  is  to  base  a  sliding 
scale  charge  per  unit  upon  the  number  of  units  used  per  horse-power 
installed  per  half  year.  Such  charge  might  be  graduated  at  id.,  ijd., 
2d.,  and  a^d. 

It  is  found  that  compared  with  a  gas  engine  using  gas  at  2S.  3d.  per 
1,000  cb.  ft,  the  cost  of  running  a  motor  at  id,  per  unit  is  considerably 
less,  in  some  cases  the  cost  is  half  that  of  gas,  in  others  the  cost  is 
approximately  the  same.  This,  however,  is  owing  to  the  motor  being 
set  to  drive  long  lengths  of  shafting  where  the  load  is  fairly  continuous 
and  heavy,  an  ideal  drive  for  a  gas  engine.  Where  the  load  is  subject 
to  great  fluctuations,  as  is  the  case  with  crane  and  hoist  driving,  the 


624  CHATTOCK:  MOTIVE  POWER  SUPPLY  [Leeds, 

motor,  even  at  2d.  per  unit,  shows  a  great  saving  over  the  gas  engine. 
This  is  owing  to  the  facility  for  stopping  the  motor  when  not  actually 
in  use,  and  starting  again  when  required.  It  is  found  that  this  cannot 
conveniently  be  done  with  a  gas  engine. 

In  order,  therefore,  to  show  a  saving  over  gas  at  the  above  figure 
per  i,ooo  cb.  ft.,  the  charge  for  current  should  vary  from  id.  to  2d, 
per  unit. 

The  amount  charged  for  rental  should  be  kept  as  small  as  possible 
consistent  with  paying  actual  expenses,  and  any  profits  required  should 
be  looked  for  from  the  sale  of  current  and  not  from  the  receipts  for 
rental. 

The  rental  should  include  the  following  items  :  — 

Interest  upon  capital  cost  of  motors  and  other  apparatus. 
Cost  of  inspecting  motors  periodically. 
Cost  of  maintenance  of  motors  due  to  fair  wear  and  tear. 
Cost  of  depreciation  on  motors. 

In  the  City  of  Bradford,  for  the  year  1902,  the  cost  of  inspection  and 
maintenance  of  motors  on  hire  amounted  to  ;£i,723,  the  H.P.  of  the 
motors  on  hire  being  2,996. 

It  would  appear  that  an  amount  of  15  per  cent,  on  the  capital  cost 
of  apparatus  is  sufficient  to  cover  all  liabilities  in  connection  with  a 
hiring  out  department,  and  to  allow  sufficient  margin  for  depreciation. 

In  conclusion,  it  is  hoped  that  the  figures  and  suggestions  given  in 
this  paper  may  be  of  interest  to  Central  Station  Engineers.  They  are 
based  upon  actual  experience  in  connection  with  the  Bradford 
Corporation  supply,  and  should  prove  useful,  especially  to  those 
Engineers  who  are  contemplating  a  motor-hiring  department. 

JJ^    ^  Mr.  A.  B.  Mountain  said  that  he  agreed  almost  entirely  with  Mr. 

Chattock.  He  was  of  opinion  that  a  supply  of  4,398  H.P.  for  motors  was 
larger  than  the  supply  in  any  other  town  in  England,  and  the  author 
would  no  doubt  say  that  the  great  success  at  Bradford  was  due  to  the 
fact  that  this  city  had  a  large  number  of  small  trades. 

Regarding  the  single-phase  question  the  speaker  thought  that  Mr. 
Chattock  was  a  little  late  in  his  criticism ;  if  he  had  made  this 
remark  three  years  ago  most  people  would  no  doubt  have 
agreed  with  him.  In  England  there  were  about  one  thousand  manu- 
facturers of  continuous-current  motors,  but  few  of  them  make 
single-phase,  and,  probably,  fewer  still  two-  or  three-phase  motors. 
There  were  thousands  of  persons  criticising  single-phase  motors 
and  advertising  continuous-current,  but  he  did  not  think  that  it  was 
wise  for  them  to  allow  themselves  to  be  carried  away.  They  had, 
rather,  to  think  of  what  was  really  right  and  suitable.  He  disagreed 
with  Mr.  Chattock  on  this  point  very  strongly. 

Referring  to  the  percentage  (10  per  cent.)  allowed  by  Mr.  Chattock 
on  the  cost  of  an  extension,  he  thought  that  there  must  have  been  an 
oversight  here.  He  did  not  consider  that  10  per  cent,  would  cover  the 
cost  of  the  extension  for  mains,  unless,  of  course,  there  were  very  special 
consumers. 


1908.] 


FROM  CENTRAL  STATIONS:   DISCUSSION. 


Further,  he  did  not  think  that  the  author  had  sufficiently  brought 
out  the  great  advantage  of  electric  motors  over  gas  engines.  There  was 
no  doubt  that,  by  getting  rid  of  shafting,  the  power  required  in  a  place 
was  enormously  reduced.  For  example :  In  a  small  works  that  he 
recently  visited  they  used  to  have  a  gas  engine  of  i6  H.P.,  but  they 
now  find  that  five  H.P.  in  motors  put  on  different  machines  would 
do  precisely  the  same  work. 

Mr.  G.  Wilkinson  said  Bradford  was  a  pioneer  town  in  electric 
lighting  and  certainly  showed  the  way  in  promoting  the  sale  of  elec- 
tricity. Like  the  previous  speaker,  he  was  very  much  struck  with  the 
second  paragraph  of  the  paper.  It  showed  that  Mr.  Chattock  had  a 
certain  amount  of  pity  for  the  community  which  has  to  put  up  with 
single-phase  motors.  ,He  himself  did  not  share  that  sentiment.  In  the 
first  place  he  would  like  to  point  out  how  very  much  more  reliable  they 
were  than  direct-current  motors.  Taking  into  consideration  the  fact 
that  the  revolving  part  simply  consisted  of  a  mass  of  iron  with  short- 
circuited  conductors,  the  advantage  certainly  rested  with  the  single- 
phase  machines  so  far  as  reliabiHty  was  concerned.  The  great  drawback 
at  present,  admittedly,  was  the  want  of  a  simple  method  of  varying  the 
speed  of  single-phase  motors.  He  had  used  this  type  for  hoists,  cranes, 
printing  machinery,  and  the  like,  and  had  found  them  very  successful. 

Mr.  Chattock  had  stated  that  the  load  factor  in  Bradford,  excluding 
traction,  was  1378.  He  presumed  that  this  did  not  represent  power, 
but  was  simply  the  load  factor  relative  to  the  motor  business.  From  the 
amount  of  the  horse-power  supplied,  he  thought  that  in  Bradford  many 
of  the  motors  were  small. 

Concerning  the  supply  of  electricity  for  large  powers  except  for 
intermittent  work,  there  was  a  very  formidable  rival  in  oil  engines.  Mr. 
Chattock  gave  a  comparison  between  electricity  at  id.  per  unit  and  gas 
at  2s.  3d.  per  1,000  cubic  feet,  but  he  did  not  mention  anjrthing  less  than 
id.  per  unit  for  electricity.  There  were  English  oil  engines  made 
which  would  give  5  or  6  H.P.  for  an  hour  for  id.,  and  there  were 
German  engines,  one  of  which  he  had  under  his  control,  working 
daily  for  practically  16  hours,  giving  9  B.H.P.  for  id.  per  hour.  They 
required  a  certain  amount  of  labour  and  attention,  but  they  had  many 
advantages.  In  the  future  we  should  have  very  keen  competition  from 
oil  engines.  There  were  now  firms  ready  to  enter  into  contracts  to 
supply  any  quantity  of  oil  as  fuel  at  35s.  a  ton. 

With  reference  to  the  extension  of  mains  in  Bradford  it  appeared 
that  the  charge  was  upon  a  basis  of  10  per  cent,  on  the  capital  outlay. 
The  paper  did  not  indicate  whether  this  was  an  annual  charge  or 
whether  it  would  run  out  when  the  interest  and  sinking  fund  expires. 
It  seemed  to  be  a  very  reasonable  figure,  but  further  information 
was  desirable.  Again,  consumers  who  used  their  motors  intermittently 
appear  to  consume  a  much  greater  number  of  units  than  did  regular 
users,  and  it  appeared  that  they  must  therefore  have  motors  too  large 
for  the  work  they  have  to  do. 

He  quite  agreed  with  the  sliding-scale  method  as  an  equitable 
means  of  charging  for  power,  and  was  quite  gratified  to  find  that 
15  per  cent,  was  sufficient  to  cover  the  cost  of  a  hiring-out   depart- 


Mr. 
Mountain. 


Mr. 
Wilkinson. 


626 


CHATTOCK:  MOTIVE    POWER   SUPPLY 


[Leeds, 


Mr. 

Wilkinson. 


Mr.  Fedden. 


Mr. 

Churton. 


ment,  and  thought  it  very  reasonable  and  a  charge  that  any  consumer 
could  afford  to  pay. 

Mr.  S.  E.  Feddem  said  that  he  could  join  issue  with  the  author 
in  regard  to  single-phase  motors.  He  had  installed  motors  up  to  80 
and  90  H.P.,  and  lately  one  of  160  H.P.,  although  he  thought  it 
most  likely  that  two-phase  motors  would  be  necessary  for  heavy 
work.  He  had,  however,  no  intention  of  abandoning  single-phase 
working  altogether  for  small  motors  on  present  single-phase  mains. 

With  regard  to  the  question  of  variable  speed  he  had  never  found 
any  demand  for  it. 

They  were  in  Sheffield  following  on  much  the  same  lines  as  in 
Bradford,  as  they  had  in  1900  only  20  motors  ;  in  1901,  71  ;  in 
1902,  109 -;  whilst  this  year  they  had  220,  which  amounted  in  all 
to  1,400  H.P. 

With  regard  to  the  price  of  energy,  they  had  always  had  in  Sheffield 
a  charge  of  4d.  a  unit  for  lighting.  Three  years  ago  it  was  2d.  a  unit 
for  power,  and  they  then  offered  consumers  lid.  per  unit,  but  nobody 
would  look  at  it.  Finally  they  arranged  to  charge  all-day  consumers 
ijd.  per  unit,  with  a  id.  per  unit  for  all-day-and-night  consumers. 
If  they  used  sufficient  units  to  make  up  50  per  cent,  of  the  horse-power 
installed,  they  allowed  them  to  come  in  at  the  ijd.  rate.  Gas  being 
only  IS.  6d.  per  i,ocx)  cubic  feet,  they  had  very  keen  competition. 

He  encouraged  the  laying  of  mains,  but  did  not  put  on  any  price  or 
percentage,  for  the  reason  that  the  local  price  of  gas  was  so  low, 
and  their  mains  were  past  most  of  the  houses  and  works.  Referring 
to  the  cost  of  generation,  Mr.  Chattock  stated  that  rates  and  taxes 
should  not  be  included,  but  he  thought  that  a  certain  percentage  of 
these  charges,  and  also  some  standing  charge  on  the  distribution  of 
the  mains,  should  be  added  to  the  cost  of  the  unit  in  addition  to  the 
items  mentioned.  He  was  rather  surprised  to  see  the  figure  given  for 
the  maintenance  of  motors.  The  cost  of  maintenance  appeared  to  work 
out  at  about  i  is.  6d.  per  H.P.  in  Bradford.  The  motors  averaged  47  H.P. 
each.  The  cost  of  maintenance  and  inspection  in  Sheffield  came  to  £7$ 
for  the  whole  of  the  motors,  or  about  3s.  per  H.P. 

He  had  not  yet  had  the  pleasure  of  a  burnt-out  armature,  but  was 
looking  forward  to  it. 

Mr.  T.  H.  Churton  said  that  he  had  had  an  opportunity  of  making  a 
comparison  of  electric  driving  and  gas-engine  driving.  In  his  works 
he  had  a  6- H.P.  Crossley  engine  and  found  that,  at  full-load,  the  cost 
was  little  less  than  ^d.  per  H.P.  hour,  and  at  normal  working  load  it  was 
about  id.  per  H.P.  hour.  It  was  necessary,  with  a  gas  engine  where 
there  was  a  variable  load,  to  have  an  engine  of  considerably  greater 
power  than  was  generally  used,  but  in  the  case  of  a  motor  it  was  not  so. 
If  a  gas  engine  were  overloaded  it  would  pull  up,  but  a  motor  could  be 
overloaded  to  a  very  much  greater  extent,  before  it  will  stop,  especially 
if  it  were  a  two-  or  three-phase  machine.  In  his  case  a  two-phase  motor 
was  actually  costing  him  less  than  the  gas-engine  did,  although  gas  in 
Leeds  cost  only  2s.  3d.  per  1,000  cubic  feet.  Unfortunately  there  was 
no  convenient  way  of  starting  single-phase  motors,  and  a  method  of 
starting  was  required  which  gave  really  no  trouble. 


1903.] 


FROM  CENTRAL  STATIONS:    DISCUSSION. 


627 


Mr.  Fynn. 


As   touching   the    competition    between  electric  driving  and  oil    Mr. 
engines,   it   must   be    noted  that   motors  could  be  placed  where  it 
would  be  impossible  to  fix  an  oil-engine  and  there  was  also  too  much 
work   involved  in  the  usei  of  oil  engines,  to  say  nothing  of  the  smell 
and  noise. 

Mr.  V.  A.  Fynn  thought  the  single-phase  motors  were  not  entirely 
satisfactory.  He  had  been  familiar  with  them  since  1893,  when 
they  came  out,  and  although  he  liked  them,  and  was  greatly  interested 
in  their  working,  he  did  not  think  that  they  answered  the  present 
requirements.  In  cases  where  only  a  few  small  motors  were  connected 
to  the  supply  mains,  the  power-factor  question  did  not  matter  very 
much.  If,  however,  one  were  concerned  with  large  powers,  the  matter 
became  more  serious  than  was  generally  believed.  At  the  Frankfort 
Exhibition  of  1891  a  motor  was  actually  shown  which  had  a  power- 
factor  equal  to  unity,  although  nobody  seemed  to  have  taken  any 
notice  of  it.  The  principle  which  was  used  in  that  motor  he  had  lately 
employed  with  various  alterations  and  improvements  in  order  to  obtain 
a  power-factor  equal  to  unity  in  a  single-phase  motor  of  his  design 
which  he  was  bringing  out,  and  which  besides  having  a  very  great 
starting  torque,  gave  promise  of  the  possibility  of  regulating  its  speed. 
A  3  B.H.P  experimental  motor  had  been  completed  which  started 
with  a  loj  H.P.  torque  and  with  a  current  simply  proportional  to  the 
full-load  starting  current. 

Mr.  W.  Emmott  said  that  Bradford  had  been  worked  for  all  it  was  Mr.Emmou. 
worth  with  regard  to  motors.  He  could  not  speak  from  the  Municipal 
Engineer's  point  of  view,  but  only  from  that  of  the  Consulting  Engin- 
eer, and  he  thought  it  was  a  good  lesson  for  some  of  the  smaller 
stations.  Much  depended  upon  the  kind  of  man  who  was  in  charge  of  a 
motor  department.  He  considered  that  with  a  gas-engine  running  up 
to  10  or  12  H.P.  it  was  cheaper  to  put  in  motors  at  2d.  per  unit.  He 
also  thought  that  15  per  cent,  was  a  large  amount  for  maintenance. 
For  himself  he  thought  12  per  cent,  a  fair  and  ample  amount.  He  gave 
some  tests  of  the  low  thermal  efficiencies  of  gas  in  various  towns  which 
he  had  experienced,  but  as  the  gas  companies  were  under  no  obliga- 
tion to  supply  gas  for  power  purposes,  the  consumer  had  no  remedy. 
This  accounted  for  the  large  gas  consumption  per  B.H.P.  which  he 
had  noted  in  many  cases,  and  was  all  in  favour  of  electro-motors. 

Mr.  W.  M.  RoGERSON  thought  that  consumers  using  lifts  and  cranes 
intermittently,  say  not  more  than  half  an  hour  at  a  time,  should  pay 
more  than  consumers  using  power  continuously. 

Mr.  H.  Dickinson  {Chairman)  did  not  agree  with  Mr.  Chattock 
that  it  was  unnecessary  to  increase  the  staff  or  plant  for  the  full  load. 
If  the  orerlapping  motor-load  grew  larger  than  the  lighting  load,  he 
would  have  to  put  in  additional  plant  to  keep  up  with  it,  and  conse- 
quently the  staff  would  have  to  be  increased  accordingly. 

Regarding  the  extension  of  mains,  on  a  basis  of  10  per  cent,  of  the 
revenue  he  thought  this  very  small,  and  remarked  that  he  would  go 
into  some  districts  for  one  per  cent.,  but  not  into  others  for  ten  per 
cent,  if  there  were  no  prospects ;  therefore  some  little  reservation  was 
necessary  on  that  point.    The  consumers  around  the  Works  were  made 


Mr, 
Kogerson. 


Mr. 
Dickinson. 


628 


CHATTOCK:   MOTIVE   POWER  SUPPLY 


[Leeds» 


Mr. 
Dickinson. 


Mr. 
Chattock. 


equal  to  consumers  in  the  outlying  districts,  unless  there  were  a  very 
big  margin  between  the  selling  prices.  At  Leeds  they  were  selling 
at  cost  price,  as,  last  year,  on  a  capital  of  £500,000,  they  made  a  profit 
of  only  ;£3,ooo.  He  did  not  think  he  could  afford  to  run  to  outlying 
districts  on  a  bare  10  per  cent. 

Referring  to  the  units  per  B.H.P.  for  last  year  at  Bradford,  which 
worked  out  at  about  450  for  every  H.P.  installed,  he  should  like  to  ask 
what  sort  of  users  they  had,  because  these  figures  did  not  at  all 
correspond  with  those  for  Leeds.  It  was  there  found  that  they  were 
getting  800  units  per  H.P.  installed.  He  did  not  know  whether  these 
motors  were  for  hoists,  but  he  thought  that  Leeds  seemed  to  be  in  a 
very  favourable  position.  In  1901  there  were  205  H.P.  installed  ; 
1902,  685  H.P. ;  and  there  were  now  1,363  H.P.  The  price  in  1901  was 
2d.,  less  5  per  cent.,  and  in  1902  it  was  2d.  to  ij^.  on  a  varying  scale. 
If  the  units  were  less  then  360  per  H.P.  it  was  2d.,  and  on  to  720  units 
per  H.P.  installed.    The  average  price  obtained  for  motors  was  i^. 

There  were  another  400  H.P.  awaiting  connection,  and  an  application 
for  500  H.P.  to  drive  a  rolling  mill  had  been  received, 

Mr.  R.  A.  Chattock,  in  reply,  said  that  he  had  not  had  much  expe- 
rience recently  with  single-phase  motors,  but  he  had  had  a  good  deal 
some  time  ago.  He  thought  that  the  motors  ran  at  a  very  excessive 
speed,  owing  possibly  to  the  high  frequency  that  was  in  general  use, 
and  that  the  efficiency  of  the  motors  up  to  about  10  H.P.  was  nothing 
like  that  which  could  be  obtained  from  direct-current  motors.  Com- 
monly the  starting  current  was  excessive,  and  affected  the  general 
supply  in  the  neighbourhood,  which  was  a  very  great  objection. 

He  was  surprised  to  hear  4hat  Mr.  Fynn  and  Mr.  Fedden  thought 
that  there  were  single-phase  motors  which  would  beat  direct-current 
motors. 

The  phenomenal  increase  in  Bradford  was  not  due  to  any  special 
advantages ;  Bradford  was  an  ordinary  city,  although  there  were  many 
trades  in  it.  Power  was  mostly  used  for  crane  and  hoist  work,  4^  and 
7  H.P.  being  the  sizes  commonly  used.  There  were  also  a  number  of 
larger  motors  (one  of  60  H.P.)  driving  various  classes  of  machinery, 
printing  works,  large  ventilating  fans  and  refrigerating  machinery.  In 
many  cases  these  motors  had  been  put  in  to  replace  gas  engines,  and 
the  reports  of  the  saving  in  cost  had  been  most  satisfactory. 

Referring  to  the  amount  of  10  per  cent,  on  the  cost  of  the  mains, 
this  amount  represented  the  actual  revenue  that  should  be  received 
from  a  proposed  consumer,  in  order  to  make  it  worth  while  incurring 
the  cost  of  the  necessary  mains.  If  the  amount  per  annum  received 
from  the  consumer  equalled  10  per  cent,  on  the  cost  of  the  mains 
necessary  to  supply  him,  he  considered  that  for  any  ordinary  extensions 
it  was  policy  to  connect  up. 

He  agreed  with  Mr.  Dickinson  that  for  very  long  extensions  in  out- 
lying districts  this  amount  should  be  carefully  considered,  and' very 
probably  increased.  In  fact,  he  thought  that,  in  getting  out  the  cost 
for  each  year,  care  should  be  taken  to  watch  that  figure  and  see  that  the 
general  percentage  of  revenue  to  the  cost  of  the  mains  was  not  getting 
too  small.  If  it  had  a  tendency  to  decrease,  then  the  10  per  Q^nt  shpuld 
be  increased  in  conformity  with  the  general  revenue. 


19(».]  FROM   CENTRAL  STATIONS :  DISCUSSION.  629 

As  regards  the  cost  of  steam  power,  as  compared  with  electric  Mr. 
power,  he  thought  that  from  150  to  200  H.P.  could  be  more  economi-  ^***"'^'^ 
cally  supplied  by  the  consumer  himself  than  by  purchasing  current 
from  a  central  station,  that  is  to  say,  as  long  as  such  power  was  used 
continuously  throughout  the  working  hours  of  the  day.  An  engine  of 
200  H.P.  was  as  economical  as  a  very  much  larger  engine  in  a 
generating  station,  and  there  were  no  distributing  charges  to  face  in 
connection  with  the  steam  supply.  There  was  a  charge  for  labour  in 
connection  with  the  running  of  the  steam  plant,  but  from  information 
he  had  received  from  mill-owners  who  had  gone  into  the  question, 
there  was  no  doubt  that  they  could  produce  steam  as  cheaply  as 
electricity  could  be  supplied  at  id.  from  a  central  station. 

With  reference  to  the  remarks  on  the  load  factor  given,  it  included 
the  lighting  consumer  as  well  as  the  private  power  consumers,  but  it 
did  not  include  the  power  for  tramways,  although  this  came  from  the 
same  station. 

Most  of  the  motors  ranged  from  i  to  10  H.P.  There  were  15,  20, 
and  60  H.P.  motors  in  use,  and  there  appeared  to  be  an  increasing 
demand  for  the  larger  size  of  motor,  as  they  were  slightly  more 
economical. 

He  was  very  much  interested  in  Mr.  Wilkinson's  remarks  on  oil- 
engines, viz.,  that  5  or  6  H.P.  could  be  obtained  for  id.  an  hour.  He 
took  it  that  this  was  at  full  load,  and  that  the  cost  of  running  an  oil- 
engine at  a  reduced  load  would  be  considerably  more.  The  great 
objection  to  oil-engines  was  the  trouble  in  starting  them  and  their 
objection  to  be  considerably  overloaded,  which  was  a  special  point  in 
favour  of  a  motor  supply.  He  also  believed  that  Insurance  Companies 
objected  to  the  storing  of  a  large  quantity  of  oil,  and  there  had  been 
trouble  in  this  respect.  He  thought  that  if  oil-engines  came  into 
general  use  the  price  of  oil  would  go  up.  Some  time  ago  he  was  trying 
some  oil  fuel,  and  from  the  figures  that  were  worked  out  he  was  satis- 
fied that  with  oil  at  2d.  per  gallon  he  could  equal  coal  at  about  i8s.  to 
19s.  per  ton. 

With  reference  to  the  question  of  continuous  users  of  electricity 
using  less  current  than  those  using  it  intermittently,  this  was  quite 
possible.  The  continuous  user  very  often  ran  his  motor  for  many 
hours  in  order  to  get  it  at  id.,  because  if  he  stopped  his  motor  he  was 
charged  at  the  rate  of  2d.  per  unit.  He  thought  it  was  best  to  base 
a  sliding-scale  charge  on  the  number  of  units  used  per  H.P.  installed. 

With  regard  to  variable  speed,  he  had  not  found  any  great  demand 
for  it.  Possibly  they  had  twenty  or  thirty  motors,  vaiying  in  size,  in 
which  this  had  been  asked  for  and  obtained,  chiefly  for  running  special 
machinery. 

He  did  not  agree  that  the  cost  of  generation  should  include  a  portion 
of  the  rents,  rates  and  taxes,  and  a  charge  on  the  mains,  although  that 
point  should  be  watched.  If  the  supply  for  motive-power  purposes 
very  much  exceeded  the  supply  for  lighting,  the  cost  of  generation 
should  be  reckoned  out  to  include  more  of  the  standing  charges  on  the 
station  and  possibly  on  the  mains,  but  as  pointed  out  the  motor  overlap 
load  was  apparently  very  small  at  present,  and  in  spite  of  the  large 


630  CHATTOCK  :  MOTIVE   POWER  SUPPLY.  [Leeds.  1908. 

Mr.  increase  in  the  number  of  motors,  it  did  not  appear  that  this  should  be 

ciiattocic       taken  into  account  for  some  considerable  time. 

The  figure  that  was  quoted  for  the  maintenance  of  the  motors,  viz., 
;£i,723,  looked  rather  high,  but  it  included  many  spare  parts,  and  also 
the  supply  of  oil  for  running  and  general  repairs,  the  cost  of  which  was 
refunded  by  the  hirer.  It  was  really  men's  wages  for  inspecting  and 
repairing  the  motors.  The  wages  that  were  paid  for  inspection  were 
higher  than  was  the  case  in  many  towns,  and  it  was  looked  upon  rather 
in  the  form  of  an  insurance.  Every  motor  was  inspected  at  least  every 
two  months,  and  most  of  them  once  a  month.  He  thought  that  the 
benefit  of  it  would  be  felt  as  time  went  on  in  the  greater  life  of  the 
motors,  because  if  they  were  left  to  look  after  themselves  they  were 
liable  to  become  very  dirty.  The  consumer  would  not  look  after  them, 
and  he  admitted  that  the  commutators  were  a  source  of  trouble  if  the 
motors  were  not  looked  after,  consequently  he  did  not  think  it  a  very 
heavy  item.  He  thought  it  would  pay  the  alternating-current  consumer 
to  look  after  his  motors  and  to  inspect  them  more  frequently.  Time 
would  show  if  this  amount  could  be  reduced  by  giving  up  inspecting 
them  so  often,  but  at  present  he  did  not  feel  inclined  to  run  the  risk  of 
doing  so. 

Mr.  Emmott  thought  15  per  cent,  on  the  capital  cost  of  the  apparatus 
was  too  great  an  amount  to  charge,  and  he  recommended  12  per  cent. 
He  (the  speaker),  however,  thought  that  the  15  per  cent,  charge  should 
be  made.  The  cost  of  motors  during  the  last  four  years  had  dropped 
by  about  30  per  cent.,  and  if  the  charge  were  12  per  cent,  it  certainly 
would  not  pay  for  the  necessary  inspection. 

With  reference  to  Sheffield  beating  Bradford  he  should  be  very 
pleased  if  they  got  ahead,  but  he  thought  that  if  the  question  of  the 
H.P.  installed  per  1,000  of  population  were  taken  into  consideration, 
Bradford  would  still  be  able  to  keep  the  lead,  although  the  increase 
was  not  so  great  during  the  last  two  years.  The  increase  in  Sheffield 
was  rather  phenomenal  on  account  of  the  supply  being  specially  pushed 
just  now.  At  the  first  everybody  was  coming  on.  Directly  people 
began  to  see  that  the  motors  could  be  obtained  cheaply  and  were  doing 
well,  they  would  all  come  on  in  a  rush,  and  in  a  large  town  where  there 
was  a  great  amount  of  power  undoubtedly  this  rush  would  be  felt 
at  first. 

In  Leeds,  Mr.  Dickinson  said,  they  were  getting  800  units  per  H.P. 
installed.  In  Bradford,  however,  there  were  not  many  motors  running 
on  a  very  heavy  continuous  load,  the  work  being  intermittent  and 
chiefly  used  in  crane  and  hoist  work.  The  staple  trade  in  Bradford 
was  woollen,  and  all  the  mills  had  theif  own  steam  plant.  There  were 
not  at  the  present  time  any  motors  in  use  for  driving  looms  or  wool- 
combing  machinery.  It  was  found  that  the  people  applied  for  motors 
for  driving  cranes  and  all  small  machinery  where  the  load  was  inter- 
mittent, and  there  was  no  doubt  that  this  accounted  for  the  sRiall 
number  of  units  that  were  used  per  H.P.  installed. 


HORIZONTAL  AND   SPHERICAL  CANDLE-POWER.  631 

ORIGINAL   COMMUNICATION. 


MEAN    HORIZONTAL   AND   MEAN    SPHERICAL 
CANDLE-POWER. 

By  Alexander  Russell,  M.A.,  Member. 

Introduction — Mean  Horizontal  Candle-power — How  the  Mean  Horizontal 
Candle-power  varies  with  the  Area  of  the  Candle-power  Curve  in 
Particular  Cases — Mirror  Effects  of  the  Bulb — Rapid  Methods  of  getting 
Mean  Horizontal  Candle-powers — Mean  Spherical  Candle-power — 
First  Graphical  Method — Mathematical  Formula — Mean  Hemispherical 
Candle-power — Second  Graphical  Method — Rapid  Method  of  getting 
Mean  Spherical  and  Mean  Hemispherical  Candle-powers— Conclusions. 

The  accurate  rating  of  glow  lamps,  Nernst  lamps,  and  arc  lamps  is  a 
matter  of  considerable  commercial  importance,  and  so  the  following 
remarks  on  the  mathematics  of  the  question  may  not  be  out  of  place  in 
the  Journal.  The  physical  side  of  the  problem,  namely,  the  quality  of 
the  light  emitted  and  the  best  standards  to  use  in  the  various  cases,  has 
not  been  touched  upon. 

English  manufacturers  as  a  rule  do  not  guarantee  that  an  8-candle- 
power  glow  lamp  gives  a  mean  horizontal  candle-power  equal  to  eight 
candles,  but  merely  that  the  mean  horizontal  candle-power  is  within 
20  per  cent,  or  so  of  eight.  They  do,  however,  guarantee  a  certain 
efficiency  with  particular  classes  of  lamps,  saying  for  example  that  their 
efficiency  at  the  start  is  3*5  watts  per  candle,  and  that  after  a  thousand 
hours  it  is  about  5  watts  per  candle.  This  method  of  rating  lamps  is 
to  be  commended,  as  it  cheapens  the  cost  of  production  and  is  quite 
fair  to  the  consumer.  By  the  candle-power  of  the  lamp  is  meant  the 
mean  candle-power  in  a  plane  perpendicular  to  its  axis,  and  this  candle- 
power  is  also  called  its  mean  horizontal  candle-power. 

Mean  Horizontal  Candle-power. 

If  from  a  source  S  we  draw  lines  equally  in  all  directions  in  a  plane 
and  make  their  lengths  equal  to  the  candle-power  in  these  directions,  then 
the  sum  of  all  these  lengths  divided  by  their  number  gives  the  mean 
candle-power  in  that  plane.  When  the  axis  of  the  lamp  is  vertical,  the 
mean  candle-power  in  the  horizontal  plane  is  called  the  mean  hori- 
zontal candle-power.  Now  many  inventors  have  tried  to  increase  the 
mean  candle-power  in  particular  planes  by  means  of  reflectors  and 
refractors,  and  some  even  think  that  they  can  increase  the  total 
quantity  of  light  given  out  by  the  lamp  by  this  means.  As  a  proof  they 
mention  that  they  have  increased  the  area  of  the  candle-power  curve  in 
particular  planes.  This  they  have  undoubtedly  done  in  certain  cases, 
but  it  does  not  follow  that  they  have  increased  the  mean  candle-power 
in  these  planes.  In  fact,  when  we  remember  that  by  doubling  the 
intensity  of  the  source  we  can  quadruple  the  area  of  the  candle-power 
curve,  the  fallacy  of  their  reasoning  is  apparent.  The  following  mathe- 
matical examples  illustrate  how  the  area  and  the  mean  value  of  the 
radius  of  the  candle-power  curve  can  vary  in  certain  cases. 
Vol.  82.  42 


\y 


632 


RUSSELL:   MEAN   HORIZONTAL  AND 


If  I   be  the  mean  value   of  radii 
angular  intervals  in  a  plane,  then — 


Tn  drawn  at  equal 


1  = 


r.  +  r,  + 


r,  d9  +  r. 


n 

tl9  4-  . 
nd9 


4-  r« 


+  r.,  d9 


\ 


2  IT 
0 


2  IT 


Now,  suppose 
the  candle-power 
curve  to  be  a  circle 
(Fig.  i),  and  let  S, 
the  source,  be  any 
p>oint  within  it 
We  may  suppose, 
for  example,  that 
the  source  is  sur- 
ounde  d  by  an 
absorbing  cylin- 
drical globe  of 
varying  thickness 
so  that  the  candle- 
power  in  the  direc- 
tion SP  is  repre- 
sented by  S  P,  and 
that  the  locus  of  P 
is  a  circle.  We 
shall  find  an  ex- 
pression for  the 
mean  candle- 
power  for  different 
positions  of  S,  sup- 
posing always  that  the  candle-power  curve  remains  the  same  circle. 

A 

and  C  A  =  R,  it  is  easy 
to 


Pig.  I. — S  is  a  source  of  light  surrounded  by  an 
unevenly  distributing  globe  which  makes  the  candle- 
power  curve  in  the  plane  of  the  paper  the  circle  A  PA'. 
Any  radius  vector  like  S  P  gives  the  candle-power  in 
that  direction. 

^  circumference  of  ellipse 

2  TT 


Mean  candle-power 


If  SP  =  r(Fig 

I),     PSA»=:0,    CS  =  a,  and( 

show  that— 

r  =  a  cos  0  -h    >/  K=  —  a=  sin  '  9, 

/.2ir 
rd9 

Hence 

1=     ^ 

2  TT 

r2^ 

1     V  R'  —  a»  sin  -  9  d9 

2  TT 

circumference  of  ellipse 

"~  2  IT  ~  * 


MEAN   SPHERICAL    CANDLE-POWER. 


633 


Where  the  ellipse  (Fig.  i)  has  S  for  its  focus  and  touches  the  circle 
at  A  and  A\ 

When  S  is  at  A, 


and  when  S  is  at  C 


I=- . CA 
=  0-637  .  CA, 

I  =  CA. 


Hence,  although  the  candle-power  curves  have  all  the  same  area, 
yet  the  mean  candle-power  diminishes  as  S  moves  from  C  to  A  by 
about  36  per  cent. 

It  is  easy  to  see  from  the  mathematical  definition  of  mean  candle- 

power  that  all  curves  of  the  family  rs=  a  +  bf{9\  where  I  /(©)  =  0, 

^  o 
have  *'  a  "  for  their  mean  candle-power. 


Fig.  2. — S  is  the  source  of  light,  and  S  P 
gives  the  candle-power  in  the  direction  S  P. 
Mean  candle-power  in  the  plane  of  the 
paper  equals  the  radius  of  the  dotted  circle. 


Fig.  3. — S  is  the  source  of  light,  and 
S  P  gives  the  candle-power  in  the 
direction  S  P.  Mean  candle-power  in 
the  plane  of  the  paper  equals  the  radius 
of  the  dotted  circle. 


In  the  examples  shown  in  Figs.  2  and  3,  S  is  the  source,  and  the 
mean  candle-power  of  S  would  be  the  same  whether  its  candle-power 
curves  were  given  by  the  curves  or  circles  shown.  The  equation  to 
the  curv^e  in  Fig.  2  is — 

r  =  a  (i  -f  sin  9)y 

and  to  the  curve  in  Fig.  3 — 

r  =  a  (i  +  i  sin  0). 
In  the  first  case  the  area  of  the  curve  is  100  per  cent,  greater  than 
the  area  of  the  circle,  and  in  Fig.  3  it  is  25  per  cent,  greater. 


634 


RUSSELL  :    MEAN    HORIZONTAL  AND 


Graphical  Construction. 

When  we  have  a  polar  diagram  of  the  candle-power  given,  an 
obvious  graphical  construction  to  find  the  mean  candle-power  is  to 
construct  a  new  polar  curve  (see  Fig.  6)  so  that — 


then — 


r,  =  r^f 


Meail  C.P.  in  given  plane  = 


/; 


rde 


2ir 

J  I    r,«  dB 
J  o 


Area  of  new  curve 

^  ir 

If  the  candle-powers  are  given  as  in  Figs.  4  and  5,  then  the  mean 
horizontal  candle-power  is  simply  the  mean  height  of  the  curve,  ue., 
its  area  divided  by  its  breadth. 


DeGRC£S 

Fig.  4. — Mean  horizontal  candle-power  curve  round  a  clear  bulb  16  candle- 
power  glow  lamp.  Note  the  great  rise  of  candle-power  at  172  degrees  due 
to  the  bulb  acting  like  a  concave  mirror  and  concentrating  the  light  on  photo- 
meter disc.    Distance  of  photometer  head  from  lamp,  about  three  feet. 


MEAN  SPHERICAL  CANDLE-POWER. 


635 


Sufficient  attention  does  not  seem  to  be  paid  by  practical  men  to 
the  extraordinary  way  in  which  the  horizontal  candle-power  of  an 
ordinary  glow  lamp  varies  in  different  directions.  In  Figs.  4  and  5 
are  shown  the  results  of  the  measurements  of  the  candle-power  of  an 
ordinary  glow  lamp  taken  at  intervals  of  every  five  degrees  in  the 
horizontal  plane.    The  tests  were  made  by  two  of  my  senior  students, 


Fig  5. — Mean  horizontal  candle-power  on  the  other  side  of  the  same  lamp. 
Note  the  mirror  effects  at  240  degrees  and  at  350  degrees. 


Messrs.  Chubb  and  Morris,  using  a  Lummer-Brodhun  photometer,  and 
they  paid  particular  attention  to  the  points  where  the  candle-power 
altered  rapidly.  Their  results. may  be  taken  as  typical  of  how  the 
horizontal  candle-power  of  an  ordinary  glow  lamp  varies  in  different 
directions.  The  sudden  variations  are  caused  by  the  far  side  of  the 
bulb  acting  like  a  concave  mirror  and  concentrating  the  light  on  the 
photometer  screen.  In  order  to  determine  whether  it  acted  like  a  lens 
or  not  a  bulb  was  cut  in  two,  but  no  trace  of  any  lens  effect  could  be 
found.  The  mirror  effect  was  very  pronounced,  an  image  of  a  distant 
lamp  being  seen  at  a  distance  from  the  glass  of  about  half  the  radius  of 
curvature.  On  taking  an  ordinary  lamp  in  your  hand  and  looking  into 
it  with  your  back  to  a  window  two  main  images  of  the  window  will  be 
seen,  one  erect  and  virtual  formed  by  the  front  part  of  the  bulb,  the 
other  Inverted  and  real  formed  by  the  back  part  of  the  bulb.  It  is  the 
back  part  of  the  bulb  that  causes  the  bright  bands  that  can  be  seen  on 
the  shades  of  glow  lamps.  On  putting  your  eye  in  line  with  a  bright 
band  coming  from  a  glow  lamp  and  moving  it  about,  the  image  of  the 
filament  will  be  seen  to  behave  in  exactly  the  same  manner  as  images 
do  in  concave  mirrors.    If  a  sheet  of  white  paper  be  moved  round  it, 


636 


RUSSELL  :    MEAN    HORIZONTAL   AND 


there  will  in  general  be  positions  in  which  bright  bands  of  light  arc 
cast  on  the  paper.  Sometimes,  especially  in  the  case  of  n-shaped 
filaments,  there  will  be  dark  bands.  These  dark  bands  are  caused  by 
one  leg  of  the  filament  obscuring  the  light  coming  from  the  other  leg. 
A  ten  per  cent,  dip  from  the  mean  is  by  no  means  unusual  in  this  case. 

When  glow  lamps  are  to  be  used  as  substandards  of  light  it  is 
necessary  to  test  them  first  by  finding  their  mean  horizontal  candle- 
power  curve.  If  the  candle-power  is  not  sufficiently  constant  for  a  ten 
degree  variation  on  either  side  of  a  given  position,  the  lamp  had  better 
be  rejected.  Having  found  a  suitable  lamp  and  having  marked 
distinctly  and  carefully  the  position  in  which  it  is  to  face  the  screen,  it 


Fig.  6. — Polar  horizontal  candle-power  curve  of  glow  lamp.  The  radius 
vector  S  P  gives  the  candle-power  in  the  direction  S  P.  Also  S  ^  =  Js  P, 
and  the  area  of  the  small  curve  divided  by  ir  gives  the  mean  horizontal  candle- 
power. 


should  then  be  run  for  a  hundred  hours,  candle-power  measurements 
being  taken  at  frequent  intervals  to  get  an  idea  of  the  shape  of  the  life 
curve.  So  far  as  constancy  is  concerned  it  is  better  to  use  low  efficiency 
lamps  as  standards,  and  if  care  is  taken  that  the  pressure  applied  to 
them  is  never  greater  than  the  marked  pressure  and  a  record  is  kept  of 
the  time  they  are  kept  burning  during  tests,  they  will  be  found  most 
satisfactory. 


MEAN   SPHERICAL  CANDLE-POWER. 


687 


In  Fig.  6,  a  polar  curve  of  the  candle-power  of  the  glow  lamp 
illustrated  in  Figs.  4  and  5  is  shown.  The  mean  horizontal  candle- 
power  was  found  by  constructing  a  new  curve,  the  lengths  of  whose 
radii  are  the  square  roots  of  the  corresponding  radii  of  the  candle- 
power  curve.  The  area  of  this  curve  divided  by  v  gives  13*5  as  the 
mean  hemispherical  candle-power  of  the  lamp,  a  result  which  was 
verified  by  taking  the  mean  height  of  the  curves  shown  in  Figs.  4 
and  5. 

As  a  rule,  not  much  attention  is  paid  to  the  mean  vertical  candle- 
power  of  ordinary  glow  lamps.  The  curve  shown  in  Fig.  7  may  be 
taken  as  typical. 


Fig.  7. — Vertical  candle-power  curve 
of  ordinary  glow  lamp. 


Fig.  8. — Vertical  candle- 
power  curve  when  a  spiral 
glass  rod  twisted  into  the 
shape  of  a  cup  is  placed 
round  a  glow  lamp. 


In  Fig.  8  is  shown  the  vertical  candle-power  curve  of  this  lamp  when 
a  spiral  rod  twisted  into  the  shape  of  a  cup  is  placed  round  it.  The 
shape  of  the  candle-power  curve  is  altered,  but  the  change  in  the  mean 
vertical  candle-power  is  very  slight. 


Rapid  Methods  of  Getting  the  Mean  Horizontal 
Candle-Power. 

When  the  lamp  is  rotated,  the  centrifugal  force  alters  the  position  of 
the  filaments  and  generally  alters  the  mean  hemispherical  caudle- 
power.  There  is  also  a  risk  of  the  filaments  breaking.  Still,  for 
rough  measurements,  the  method  is  a  good  one. 

Another  method  is  to  use  four  equal  pieces  of  looking-glass  cut  from 
the  same  strip.    Two  of  these  pieces  inclined  to  one  another  at  120 


688 


RUSSELL:    MEAN   HORIZONTAL  AND 


degrees  are  placed  behind  the  standard  lamp,  and  an  exactly  similar 
arrangement  is  placed  behind  the  lamp  being  tested.     If  then  the 

candle-power  of  the  lamp  being 
tested  is  approximately  the  same 
as  that  of  the  standard  and  the 
mean  horizontal  candle-power  of 
the  standard  is  accurately  known, 
we  get  by  one  reading  an  ap- 
proximation to  the  mean  of  three, 
and  so  time  is  saved.  Great 
accuracy,  however,  is  not  obtain- 
able by  this  method  if  only  one 
reading  is  taken,  as  variations  of 
five  per  cent,  can  be  obtained 
by  rotating  the  lamp  into 
different  positions,  these  varia- 
tions being  mainly  caused  by  the 
positions  of  the  bright  bands. 

Experiments  were  made 
with  diffusive  reflectors,  but  in 
no  case  could  we  make  sure  of 
obtaining  a  five  per  cent,  accu- 
racy by  one  reading.  Better 
results  would  probably  be  ob- 
tained by  using  uniform  ground- 
glass  cylindrical  chimneys  to 
put  round  the  tamps  when  being 
tested. 

Mean  Spherical   Candle- 
power. 

If  we  draw  from  the  source, 
equally  in  all  directions,  lines 
whose  lengths  are  proportional 
to  the  candle-power  in  these 
directions,  then  the  mean  value 

of  the  lengths  of  all  these  lines  is  the  mean  spherical  candle-power. 

If  ^1,  ra  .  .  .  r„  be  the  intensity  of  the  light  in  the  various  directions, 

then — 


Fig.  9. — The  revolution  of  SPA 
about  S  A  produces  the  candle-power 
surface.  Make  a  new  curve  S  p  a  so 
that  S  ^  =  l/^T.    Then    the    mean 

■?  V 

spherical  candle-power  =  ^—  ,  where 

4  *" 
V  is    the    volume   generated    by  the 
revolution  oi  Sp  a  round  S  a.     Mean 
spherical  candle-power  =  0125  S  A. 


M.S.C.P.  = 


r,  -h  ^2  + 


+  rn 


^  r  dut 

where  du  stands  for  a  very  small  solid  angle. 
Hence,  if  we  construct  a  new  surface  so  that— 


Tj^::  rh* 


MEAN  SPHERICAL  CANDLE-POWER. 


M.S.C.P.  = 


then — 

47r' 

where  V  is  the  volume  of  this  new  surface. 

It  will  be  seen  that  an  exact  solution  of  the  general  problem  is 
complicated.  When,  however,  as  is  generally  permissible  in  practice, 
we  may  suppose  that  the  extremities  of  all  the  lines  representing  the 
candle-powers  lie  on  a  surface  of  revolution,  various  simple  graphical 
methods  may  be  given  to  find  the  main  spherical  candle-power. 


Fig.  10. — S  P  A  is  the  polar  curve  of  candle-powers  in  directions 
below  the  horizontal  in  a  vertical  plane.  If  the  top  polar  curve  be 
similar,  then  the  mean  spherical  candle-power  =  0589  Si4. 


First  Graphical  Method. 

We  first  find  by  experiment  the  polar  curve  SPA  (Fig.  9),  whose 
revolution  produces  the  candle-power  surface.  We  then  construct 
a  new  curve  S^a  so  that — 

S^  =  SP^- 

It  follows  that  the— 

S  P  rfu>  +  .  .  . 


M.S.C.P.  =  ■ 


47r 
_  S^3  rfitf  -h  .    .   . 

=  3V 
4ir 

=  -3-  X  2  TT  A  X  Area  S/>  o, 

4ir 

where  h  is  the  perpendicular  distance  of  the  centre  of  gravity  of  the 
area  Spa  from  SA« 


640 


RUSSELL  :    MEAN   HORIZONTAL  AND 


For  example,  in  Fig.  9  the  curve  Spa  is  a  circle.     Hence  in  this 
case  the — 


M 


S.C.P.  =  ^^  X  2  IT  ( --   )  X  -  ( — -J 

47r  ^3^/  2X2/ 


=  1.SA. 

Similarly  in  Fig.  10,  where  Spa  is  a  circle  (only  half  the  curve  is 
drawn) — 

M.S.C.P.  =  —    X2irRXirR=' 
47r 

=  15^3 

2 

=  i^SA 
16 

=  0*5890  S  A. 


^\ 

5 

^^^^ — ""■^— — — _ 

w-^r 

\  \/^ 

-V 

A 

'^'i 

Fig.  II. — Construction  for  finding  the  directions 
in  which  to  measure  the  candle-powers  whose 
mean  value  will  give  us  the  mean  spherical  candle- 
power.  S  At  the  lower  radius  of  a  circle,  is  divided 
into  any  number  of  equal  parts,  and  through  the 
middle  points  of  these  equal  parts  lines  are  drawn 
perpendicular  to  S  /I.  S  Pt^  S  Pa,  etc.,  are  the  re- 
quired directions. 


Another  Expression  for  the  M.S.C.P. 

With  the  source  S  as  centre,  describe  a  sphere  (Fig.  11)  of  radius  R. 
Divide  the  vertical  diameter  of  this  sphere  into  any  number  of  equal 
parts,  and  through  the  points  of  section  draw  places  perpendicular  to 


MEAN   SPHERICAL  CANDLE-POWER.  641 

this  diameter,  then  these  planes  will  intersect  zones  of  equal  area  on 
this  sphere.  This  follows  from  elementary  mensuration,  since  the  area 
of  the  zone  of  a  sphere  is  2  ir  R  /r,  where  h  is  the  perpendicular  distance 
between  its  two  bounding  planes.  Now,  if  we  take  the  mean  value  of 
the  candle-powers  in  the  directions  of  all  the  radii  drawn  to  one  of 
these  zones  and  do  the  same  for  all  the  others,  the  mean  of  all  these 
results  will  give  us  the  mean  spherical  candle-power. 
For  the  case  of  a  surface  of  revolution,  if  R  =  w  // — 

M.S.C.P.  =  ""^  +  "^Jt---- + ''- 
211 


—  2R 

"    2R* 


Now      A  =  R  tfO  cos  9, 


M.S.C.P.  =  i         rco^QdQ 

~  2 


2 
which  is  a  simple  formula. 

For  example,  if  the  polar  curve  of  candle-power  be  the  semicircle 
of  spa  in  Fig  9,  and  a  similar  semicircle  above  the  horizontal,  then 

the  M.S.C.P.  =  0-5.8  o. 
Similarly,  if  it  were  the  circle  half  of  which  is  shown  in  Fig.  10, 


M.S.C.P.  =  i         2R 


the  M.S.C.P.  =  i         2  R  .  cos'Bde 


=  07854  .  S  o. 

The  equations  to  the  curves  shown  in  Figs.  2  and  3  are  of  the 
form — 

r  ^  a  -h  6  sin  0. 

Hence  the  M.S.C.P.  of  the  surfaces  of  revolution  of  which  they  are 
sections — 

IT 
2 

(a  -\-  b  sin  9)  cos  9  d9 


=»J( 


642  RUSSELL:  MEAN   HORIZONTAL    AND 

The  curves  shown  in  Fig.  12  arc  parts  of  circles ;  in  this  case — 

M.S.C.P.  =  0-555  •  O  A. 

In  Fig.  2  the  ratio  of  the  two  hemispherical  candle-powers  is  as 
one  is  to  three. 

Mean  Hemispherical  C.P. 

In  this  case  we  only  take  the  mean  value  of  the  candle-power  over 
a  hemisphere.    The  formula  is — 


r  ' 

H.C.P.  =         xd9, 
J  0 


For  example,  in  Figs.  2  and  3- 


Upper  H.C.P.  =  a  —  i  6. 
Lower  H.C.P.  =  a  +  i  6. 


Fig.  12. — The  revolution  of  the  polar  curves 
shown,  which  are  parts  of  circles,  gives  us 
the  candle-power  surface.  Mean  spherical 
candle-power  =  0555  OA. 


Second  Graphical  Method. 

Having  given  the  polar  curve  of  candle-power  APBC  (Fig.  13) 
construct  a  new  curve  so  that— 


MEAN  SPHERICAL  CANDLE-POWER, 
then  the  area  of  this  new  curve  gives  the  M.S.C.P.     For — 


613 


Area 


of  Curve  =  i   I     o 


2 

p'  dB 

TT 
2 


/•  +  -. 
=  i         xdB  ,  z=z  M.S.C.I 


Fig.  13.— O  is  the  source  of  light  and  AP  BC\^ 
the  polar  curve  of  candle-power.  Make  O  p  =i 
J~d  N  and  construct  the  curve  locus  of  p.  The 
mean  spherical  candle-power  ^  the  area  of  the 
small  curve. 


Rapid  Methods  of  Finding  M.S.C.P.'s. 

The  following  approximate  methods  will  be  found  of  practical  value. 
The  theory  will  be  best  understood  by  considering  a  particular  case. 
Divide  a  sphere  described  round  the  source  as  centre  into  eight  equal 
zones  (Fig.  11).  Through  the  centres  of  the  equal  parts  into  which  the 
radius  is  divided  draw  perpendiculars  meeting  the  surface  in  P„  P,,  P3, 
and  P4  respectively,  and  suppose  that  corresponding  lines  are  drawn  for 
the  upper  hemisphere.  Then  we  may  assume  that  the  candle-powers 
in  the  directions  S  P„  S  P.,  etc.,  are  all  equally  important 


644 


Hence 


RUSSELL  :    MEAN    HORIZONTAL  AND 
M.S.C.P.  =  ^  t.^-_+_i  - +_^B. 


where  r„  r,  .  .  .  are  the  intensities  of  the  light  in  the  directions 
S  P„  S  Pa.  .  .  .  The  lower  hemispherical  candle-power  would  be  given 
by  the  approximate  formula — 


Lower  H.C.P.  = 


—  ^»  +  ^»  +  ^3  H-  r^ 


If  we  find  the  angles  of  depression,  S  P„  S  P,  .  .  .  once  for  all,  then 
we  can  take  these  as  standard  directions.  The  mean  spherical  candle- 
power  can  be  got  directly  by  this  method  without  any  graphical  con- 
struction. 

If  the  lower  radius  be  divided  into*  2  n  portions,  then  the  angles  are 
given  by  the  equations — 


cose.  =  i--. 


Cos  Oa  =  I  — 


Cos  0„  =  I  — 


2« 

2W  —  I  I 

2 «  2n 


If  radii  be  drawn  making  angles  ±  G„  with  the  horizontal,  and  if  l„ 
and  V^  be  the  intensities  of  the  light  in  these  directions,  then — 


M.S.C.P.  = 


I.  +  I.  + 


+  I,'  +  I,'  + 


Ix  +  I,  + 


Upper  H.C.P.  = 

Lower  H.C.P.  =  ?i'  ±  ^^^]>-'  '  '. 

The  following  are  the  values  of  0„  9,,  etc.,  when  2,  4,  6,  8,  10,  or  20 
measurements  of  candle-power  arc  to  be  made  : — 


r— 

Number  of 
Measurements. 

Angles  of  Depression  or  Elevation  from  Horizontal  in  Degrees. 

2 

30 

4 

14-5,  48-6 

6 

96,  30,  56-4 

8 

7-2,  22,  387,  61 

10 

57,  17-5.  30.  44*4»  64*2 

20 

2*9,  8*6,  14-5,  2o*5,  267,  33-4,  40-5,  48-6,  582,  71-8 

MEAN   SPHERICAL   CANDLE-POWER. 


645 


Approximations  to  the  mean  spherical  candle-power  of  any  required 
accuracy  can  thus  be  obtained  by  measuring  the  candle-powers  in  the 
directions  of  the  angles  given  above  and  taking  the  arithmetical  mean 
of  the  results. 

In  order  to  illustrate  the  accuracy  of  these  approximations  the 
following  numerical  examples  have  been  worked  out : — 

In  Fig.  lo  the  lower  hemispherical  candle-power  of  the  polar  curve 
SAP  comes  out  as  follows  : — 


Number  of  Measurements. 

Lower  H.C.P. 

I 

06495 

2 

0-5979 

3 

0*5924 

4 

05904 

5 

0-5901 

lO 

'  0-5893 

Infinite 

05890 

The  first  approximation  is  simply  got  by  measuring  the  candle- 
power  at  30  degrees,  the  next  by  taking  the  mean  of  the  values  at  14*5 
and  at  48*6  degrees  respectively,  and  so  on. 

In  this  case  the  mean  of  the  candle-powers  in  directions  9*6,  30  and 
56*4  would  have  been  sufficiently  accurate. 

The  following  are  the  approximations  to  the  lower  hemispherical 
candle-power  of  the  polar  curve  S  P  A  in  Fig.  9. 


Number  of  Measurements. 

Lower  H.C.P. 

I 

01 250 

2 

0-2188 

3 

02359 

4 

02422 

5 

0*2450 

10 

0*2500 

Infinite 

0*2500 

646  RUSSELL  :    MEAN  CANDLE-POWER. 

Many  other  examples  have  been  worked  out,  and  it  has  been  found 
that  the  mean  of  five  observations  at  angles  of  57,  17*5,  30,  44*4,  and 
64*2  are  quite  sufficient  for  practical  requirenients. 

Even,  however,  when  theoretically-accurate  methods  like  Rousseau's 
or  the  graphical  methods  we  have  described  are  employed,  it  is  always 
best  to  measure  the  candle-powers  in  the  directions  given  above  for  the 
tenth  .approximation  and  not  at  ten  equal  angular  intervals,  because  in 
this  latter  case  undue  importance  is  attached  to  measurements  at  60, 70 
and  80  degrees.  As  a  rule,  an  error  in  the  measurement  when  the 
angle  of  depression  is  ten  degrees  is  much  more  serious  than  when  the 
angle  of  depression  is  eighty  degrees. 

The  points  to  which  attention  is  called  in  this  paper  are  the  follow- 
ing :— 

1.  The  bulbs  of  glow  lamps  act  like  concave  mirrors  producing 
bands  of  light  in  particular  directions.  Dark  bands  are  produced  when 
a  vertical  portion  of  the  filament  is  parallel  to  another  portion  of  it- 
These  effects  produce  very  rapid  azimuthal  variations  of  the  light. 

2.  In  determining  the  mean  hemispherical  candle-power  of  glow 
lamps,  when  no  reflectors  or  diffusers  are  used,  a  large  number  of 
observations  must  be  made.  This  number  may  be  reduced  by  using 
suitable  reflectors  or  diffusers.  If  we  rotate  the  lamp,  besides  the  risk 
of  the  filament  breaking,  tbe  centrifugal  force  must  alter  its  shape,  tluis 
altering  the  total  distribution  of  the  light  in  space. 

3.  When  glow  lamps  are  used  as  standards  it  is  of  vital  importance 
to  study  the  horizontal  candle-power  curve  before  choosing  and  mark- 
ing the  direction  in  which  they  are  to  face  the  photometer  screen. 
Neglect  of  this  precaution  even  with  c\-fi\a,mGnt  lamps  leads  to  large 
errors.  As  a  rule  the  plane  of  the  filament  is  perpendicular  to  the 
axis  of  the  bench.  The  mean  horizontal  candle-power  curves  got  by 
comparing  a  lamp  with  two  standards  of  different  powers  may  show 
distinct  variations  due  to  the  relative  mirror  effects  of  the  bulb  being 
different  at  varying  distances  of  the  photometer  screen  from  the  lamp. 

4.  Several  simple  formulae  and  graphical  constructions  are  given  for 
determining  the  mean  spherical  and  the  mean  hemispherical  candle- 
power  of  sources  of  light. 

5.  The  simplest  practical  method  of  determining  the  mean  lower 
hemispherical  candle-power  of  an  arc  lamp  is  to  measure  its  candle- 
power  in  directions  making  angles  of  57,  17*5,  30,  44*4,  and  64*2 
degrees  with  the  horizontal,  and  taking  the  mean  of  the  results.  The 
easiest  way  of  drawing  these  angles  is  by  the  graphical  construction 
indicated  in  Fig.  11.  If  greater  accuracy  is  required,  the  same  thing 
can  be  done  in  several  vertical  planes  passing  through  the  axis  of  the 
lamp  and  the  mean  of  the  results  taken. 


JOURNAL  i-Si^Sig: 

^^       •.  OP  THB 

'^'^  INSTITUTION  OF 

ELEOTBIOAL   ENGINEEBS, 

LATE 

TQS  SOCUTT  OF  TBLE6I(iPH-Ell6niBERS  AHD  EI.EGTI(ICIAHS. 

FOUNDED  1871.     INCORPORATED  1883. 

INCLUDING 

ORIGINAL   COMMUNICATIONS   ON  TELEGRAPHY  AND 
ELECTRICAL  SCIENCE. 


PUBUSHXD  UNDER  THS  SUPBBVISION  OF  THX  BDrrDfO  OOMKITTBE, 

AND  EDITED  BY 
W.  G.   MCMILLAN,  SECRETARY. 


Xondon: 
R.  AND  F.  N.  SPON,  Limited,  125,  STRAND,  W.C. 

Hew  Vorft: 
SPON  and  chamberlain,  123,  LIBERTY  STREET. 


PRICE  FIVE  SHILLINGS. 


"S.C.C."  TROUOHINQ 

FOR  SOLID  SYSTEM, 

Suitable  for  Higti  or  Low  Tonsion  Cables. 

witi,  '^rJ^T  "'  ^^^^'^'''fi  oompo«d  of  cem«nt  concrete 
m  n«.ti„/  "T  •  ^""'''^^^    *"    't.    '•>«    -teel    core   7^. 

minating  .„    end   pieces   »hich   form   the   face,  of  Bocklt 

lengths  In  laying  the  tronghing  the  end  piece,  ^ 
firmly   attached  to  each    other   by   n.e,^e  of  a   ac«w  IT 

fixed  in  "TIT  '""''*'  '**"  troug^i„g  and  entering  „°t 
fixed  „  the  cement  wall  of  the  .ocket.  avoiding  the 
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iKYsmnTr.  "T;  "^^  ""*•  "''  -■""*•  ^-  HIGH 
TENSION   Cablei.  the  n,eta]  end,  are  .o  arranged  Zb^TIi 

perfect   metallic   bond  i.  formed   between  the  .teel  core, 

of    -ucce,«ve    lengths,    the    troughing    thu,    providing   a 

of  bonded   cast   iron    or    steel    troughing   at   coa.ideratlv 

leas  coHtt 


For  Prices  and  Particufsrs  apply  to— 

THE  STEEL  CORE  CONCRETE  CO.,  LTD., 

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JOiURNAL 

OF  THE 

^nsiiiuiian  oi  (f  Itdmal  ^n^mms. 

Founded   1871.   Incorporated   1883. 


Vol.  32.  1903.  No.  162. 


GLASGOW  LOCAL  SECTION. 


A  STUDY  OF  THE  PHENOMENON  OF  RESO- 
NANCE IN  ELECTRIC  CIRCUITS  BY  THE 
AID    OF    OSCILLOGRAMS.* 

By  M.  B.  Field,  Member. 

(Paper  read  at  Meeting  of  Section,  February  io//r,  1903.) 

Three  factors  are  generally  essential  to  enable  an  intelligent  in- 
vestigator to  satisfactorily  complete  any  experimental  research,  viz., 
time,  inclination,  and  apparatus. 

During  the  last  two  years  I  have  been  in  the  enviable  positioa  of 
having  at  my  disposal  plant  and  apparatus,  from  which  by  careful 
study  many  important  and,  I  believe,  little  understood  phenomena 
might  be  investigated.  The  inclination  on  my  part  to  make  the  best 
use  of  the  opportunity  afforded  certainly  was  not  wanting ;  but  the 
small  quantum  of  available  spare  time  has  hindered  me  from  bringing 
to  a  satisfactory  termination  several  investigations  on  which  I  have 
been  at  work. 

As  in  future  I  shall  not  have  in  the  same  way  facilities  for  con- 
tinuing this  work,  I  venture  to  lay  before  you  in  all  their  incomplete- 
ness certain  results  I  have  arrived  at,  and  to  ask  you  to  consider  these 
as  mere  suggestions,  which  may  act  as  an  incentive  to  some  other 
fortunate  investigator,  who  may  have  the  time,  apparatus,  and  inclina- 
tion necessary  for  completing  the  work. 

My  subject  is  more  particularly  some  aspects  of  electrical  resonance 
which  occurred  to  me  on  observing  the  shape  of  the  E.M.F.  wave  of 
the  2,500  kw.  generators  of  the  Glasgow  Corporation  Tramways 
Department.  These  curves  were  depicted  on  the  tracing  desk  of  one 
of  those  beautiful  instruments  invented  by  Mr.  Duddell,  viz.,  the  high 
frequency  pattern  of  oscillograph. 

*  This  Paper  was  also  read  in  abstract  in  London  on  March  12th,  1903, 
and  was  discussed  jointly  with   Messrs.  Constable  and   Fawselt's   Paper, 
**  Distribution  Losses  in  Electric  Supply  Systems,"  at  Meetings  of  March  12th, 
26th  and  April  23rd,  1903.    See  pages  734,  740,  and  762. 
Vol.  82.  43 


648       FIELD  :  A  STUDY   OF  THE   PHENOMENON  OF      [Glasgow, 

At  first  I  contented  myself  with  merely  tracing  on  paper  the  curves 
thrown  upon  the  desk  of  the  apparatus.  When,  however,  I  wished  to 
obtain  curves  which  were  to  play  an  important  part  in  some  of  the 
official  tests  of  the  Glasgow  plant,  I  considered  this  method  too 
inaccurate,  and  had  constructed  several  special  dark  slides  in  which  a 
bromide  paper  or  sensitive  film  could  be  stretched  round  a  glass 
shaped  to  the  proper  curvature,  and  by  means  of  which  records  could 
be  taken  photographically  and  the  human  element  obviated.  These 
dark  slides  were  cheap  to  construct,  and  very  useful,  and  were  used 
almost  entirely  in  the  experiments  I  am  about  to  describe. 


.*. * f *- 


W~  ttB 


iji 


..9 ± JL •.!_ 


.!r 


•e 


Fig.  I. 


Fig.  I  is  a  drawing  of  the  dark  slide,  which  is  self-explanatory.  In 
using  these,  of  course,  all  stray  light  must  be  screened  off  to  obtain  the 
best  results;  and  in  this  connection  I  found  it  useful  to  employ  a 
screen  (S,  Fig.  2)  to  cut  off  all  light  from  the  bright  lacquered  parts  of 
the  oscillograph.  Many  of  these  parts  are  best  painted  with  a  dead 
black  paint,  while  it  is  of  the  highest  importance  to  entirely  cover  the 
bright  steel  face  containing  the  saw-cuts  in  which  the  vibrating  strips 
are  set.  I  found  it  advantageous  to  make  several  slight  modifications 
of  this  kind  in  the  apparatus  as  supplied  by  the  makers  in  order  to 
obtain  the  best  results  with  the  dark  slides  above  mentioned. 


19(^0 


RESONANCE  IN  ELECTRIC  CIRCUITS. 


649 


It  may  be  of  interest  to  call  attention  here  to  a  few  of  the  idiosyn- 
crasies of  the  type  of  oscillograph  employed. 

In  the  first  place,  I  experienced  considerable  difficulty  due  to  the 
shifting  of  the  zero  of  the  vibrating  mirror.  The  apparatus  contains  a 
fixed  mirror  which  gives  a  fixed  zero  line,  and  it  is  necessary  to  adjust 
each  of  the  vibrating  mirrors  so  that  the  base  line  (they  project  when 
no  current  is  flowing  through  them)  coincides  with  the  fixed  zero  line. 
After  the  strips  have  been  in  circuit  for  a  short  while,  however,  I  found 
frequently  that  the  zero  line  had  shifted,  which  produced  the  apparent 
result  of  larger  positive  half-waves  than  negative  half-waves,  or  vice 
versa.  Again,  there  is  a  tendency  for  the  cam  which  vibrates  the 
mirror  to  wear,  and  the  greatest  wear  occurs  towards  the  end  of  the 
motion,  since  here  the  pressure  on  the  cam  is  greatest.  This  wear 
afiFects  the  horizontal,  but  not  the  vertical,  displacement,  the  latter  still 
being  directly  proportional  to  the  current  flowing.  In  some  cases, 
therefore,  where  the  positive  and  negative  Half-waves  were  obviously 


Fig.  2. 


identical,  I  foimd  it  advantageous  to  apply  a  correction  in  the  follow- 
ing way : — Two  lines  were  drawn  parallel  to  the  fixed  zero  line  touch- 
ing the  highest  point  of  the  positive  and  negative  waves ;  the  distance 
between  these  lines  was  halved  and  a  corrected  zero  line  drawn  in ; 
the  positive  half- wave  was  then  reversed  and  substituted  for  the 
negative  half,  thus  almost  entirely  eliminating  the  above-mentioned 
effects.  This,  of  course,  would  not  be  permissible  where  the  positive 
and  negative  half-waves  were  of  different  shape.  I  may  say  that  all 
the  curves  here  reproduced  have  been  uncorrected  in  this  manner. 

Another  difficulty  I  experienced  was  due  to  the  violent  hunting  of 
the  oscillograph  motor  when  running  under  abnormal  conditions. 
Under  these  circumstances  two  distinct  waves  would  be  apparent  on 
the  photograph,  representing  the  limiting  positions  of  the  actual  wave 
which  the  projection  of  on  the  screen  was  shifting  backwards  and 
forwards  with  great  rapidity,  instead  of  being  stationary,  as  it  should 
have  been. 

Sometimes  this  hunting  was  caused  by  the  variation  of  load  on  the 
oscillograph  motor  (the  tension  of  the  spring  controlling  the  mirror 
varying  from  zero  to  a  maximum  in  each  revolution). 

Curve  I.  represents  the  E.M.F.  curve  of  the  system  under  normal 
load  conditions,  with  one  2,500  kw.  generator  only  running  on  the  load, 
and  supplying  245  amperes  per  phase.  The  generators  are  6,500  volt, 
3-phase,  75  r.p.m.  macHines,  with  stationary  armatures  having  two 


650       FIELD:  A   STUDY   OF  THE   PHENOMENON  OF      [Glasgow, 

slots  per  pole  per  phase,  and  40  poles.  Curve  I,  as  also  practically  all 
oscillograms  reproduced  in  this  paper,  was  taken  from  the  low-tension 
side  of  a  bank  of  transformers  in  one  of  the  sub-stations  ;  there  were 
thus  a  bank  of  transformers  and  a  high-tension  3-core  cable  intervening 
between  the  oscillograph  and  the  generator  terminals. 

I  fully  recognise  that  it  would  have  been  more  to  the  point  had 
some  of  my  measurements  been  made  in  the  high-tension  circuit  itself. 
I  even  constructed  a  resistance  to  insert  in  one  of  the  legs  of  the 


Fig.  3. 


Curve  I. — E.M.F.  Wave  of  Generator 
on  normal  traction  load,  245  amps,  per 
phase. 


armature  winding,  and  took  a  tapping  off  one  of  the  coils  near  the 
neutral  point,  as  shown  in  Fig.  3.  It  was  my  intention  to  connect  the 
neutral  point  of  the  generator  to  earth  during  these  experiments  in 
order  to  secure  safety,  it  being  normally  insulated  from  earth.  I  had 
not,  however,  the  same  facilities  in  the  power-house  as  in  the  sub- 
station, and  unfortunately  did  not  conduct  any  experiments  in  the 
former  place. 

The  arrangement  generally  adopted  was  that  shown  in  Fig.  4 — 


Fig.  4, 

The  transformer  groups  consist  each  of  three  200  kw.  single- phase 
transformers  connected  A  —  system,  and  loaded  on  rotary  converters. 
The  high-tension  cables  are  as  follows  ; — 


To  Sub-station  A 

4  —  3-core 

•15  in. 

Length 

=  4849  yards  each. 

II 

B 

4  —  3-core 

•I  in. 

„ 

=  4i775 

ft 

i» 

C 

4  —  3-core 

•I  in. 

II 

=  5>899 

f* 

ff 

D 

4  —  3-core 

•I  in. 

II 

=  2,286 

If 

II 

E 

4  —  3-core 

•15  in. 

II 

^5i6o5 

II 

An  examination  of  Curve  L  will  show  at  a  glance  that  there  are 
harmonics  of  a  high  order  present  in  the  wave  form.     Curve  II. 


I 


1903.]  RESONANCE   IN   ELECTRIC   CIRCUITS.  661 

represents  the  voltage  and  current  wave  forms  taken  from  the  low- 
tension  side  of  one  of  the  200  kw.  transformers  partially  loaded  on  a 
water  resistance.  It  will  be  noticed 
that  for  clearness  the  current  wave 
has  been  reversed,  that  there  is 
apparently  no  phase  displacement, 
and  that  the  harmonics  of  the 
current  wave  follow  closely  those 
of  the  E.M.F. 

Assuming  we  can  represent  the 
E.M.F.   wave  by  the  expression 

E  =r  2  E,  sin  (2  ir  /  n  /  +  e-,)  .     .     (i)      „  Curve  II.-E.M  F.  and  Current 
^  ^  '      Waves  from  Transformer  on  water 

n  being  the  natural  frequency  of  the      ^o^^- 
system,   i.e.,  25  cycles  per  second, 

and  the  summation  being  extended  to  all  terms  obtained  by  giving  i 
successive  integral  values  from  i  upwards,  then  the  true  voltmeter 
reading  of  E,  or  the  effective  volts,  will  be — 

yn? (2) 

^     2 
and  provided  the  water  load  acts  as  a  true  non-inductive  resistance, 
and  one  without  capacity,  i.e,  provided  no  periodic  storage  and  dis- 
charge of  energy  occurs  in  the  water  resistance,  the  current  will  be 
expressed  by — 

■j^  2  Erf  sin  (2  IT  J  w  /  +  ^0 (3) 

and  the  true  ammeter  reading  by  5V     y^ (^^ 

The  products  of  the  ammeter  and  voltmeter  readings  will  then  be — 

/r2(E.') (5) 

The  instantaneous  value  of  the  watts,  obtained  by  multiplying  the 
instantaneous  values  of  voltage  and  current  strength,  is — 

i|sE,sin(2xi»/  +  e,)p (6) 

the  average  value  of  this,  or  the  true  wattmeter  reading,  is,  of  course, 
again  represented  by  the  expression  (5) ;  in  other  words,  if  the  load  be 
a  pure  ohmic  resistance,  the  product  of  true  volts  and  true  amperes 
represents  true  watts,  no  matter  how  irregular  the  wave-shapes  may  be. 

Now  the  value  of  (2)  may  be  obtained  from  the  oscillogram  of  the 
voltage,  by  taking  the  square  root  of  the  average  value  of  the  squares 
of  a  number  of  equi-distant  ordinates. 

Similarly  the  value  of  (4)  may  be  determined  from  the  current 
oscillogram. 

Multiplying  these  together  we  obtain  the  value  of  (5). 

The  average  value  of  (6)  may  be  determined  by  first  multiplying 
the  ordinates  taken  from  the  current  and  voltage  oscillograms,  and  then 
taking  the  mean. 


662       FIELD:  A  STUDY  OF  THE  PHENOMENON  OF     [Glasgow, 

To  test  the  water  load,  as  also  the  oscillograph,  I  obtained  arith- 
metically the  values  of  (2),  (4),  (5),  and  the  average  value  of  (6),  as 
described  from  the  oscillograms,  and  in  every  case  obtained  agreement 
within  I 'per  cent. 

It  is  clear  that,  had  the  load  possessed  any  properties  of  the  nature 
of  self-induction  or  capacity,  or  if  such  factors  existed  in  the  oscillo- 
graph itself,  such  agreement  would  not  have  been  obtained. 

It  was  natural  to  inquire  what  effect  the  harmonic  or  ripple  in  the 
E.M.F.  wave  would  have  on  the  voltage  at  the  rotary  D.C.  brushes. 
To  show  this,  I  drove  the  oscillograph  motor  from  the  rotary  slip- 
rings,  connecting  one  strip  across  the  D.C.  brushes,  and  one  strip 
between  one  slip-ring  and  one  D.C.  brush  (see  Fig.  5). 

The  result  was  Curve  III.  A  distinct  ripple  was  observable  in  the 
D.C.  voltage  under  normal  load  conditions,  and  by  comparing  it  with 
the  wave  length  of  the  undulating  wave  we  find  the  number  of  ripples 


fOOCH 


000-^^^*— 0000 — H^ 


Fig.  5. 


Curve  III.— D.C.  Voltage  of 
Rotary  on  no  Load  and  E.M.F. 
between  one  D.C.  brush  and 
slip-ring. 


in  the  D.C.  voltage  per  period  is  12  ;  in  other  words,  there  is  an 
alternating  E.M.F.  of  300  cycles  superimposed  upon  the  D.C.  voltage 
of  500  volts. 

It  is  clear  that  the  E.M.F.  between  one  slip-ring  and  one 
commutator  brush  will  be  an  undulating  E.M.F.  either  wholly  positive 
or  wholly  negative.  If  the  negative  D.C.  brush  is  at  zero  potential, 
and  provided  the  rotary  is  on  load,  and  the  brushes  are  in  the  neutral 
position,  clearly  every  other  point  in  the  armature,  if  not  at  zero 
potential,  must  be  between  zero  and  the  potential  of  the  -h  D.C.  brush. 
Now,  each  slip-ring  becomes  connected  directly  to  the  -h  and  —  brush 
alternately  once  per  cycle,  hence  shape  of  wave. 

Until  I  saw  this  experiment  I  had  half  doubts  that  the  ripples  in  the 
A.C.  voltage  were  introduced  by  the  oscillograph  itself.  When,  how- 
ever, I  ran  a  rotary  as  a  double  current  generator,  self-excited,  driving 
it  by  means  of  its  starting  motor,  the  D.C.  voltage  shown  by  the 
oscillograph  was  a  perfectly  straight  horizontal  line,  and  the  A.C.  wave 
was  entirely  devoid  of  ripples  except  of  a  very  much  higher  frequency 
and  small  amplitude.*    (See  Curve  IV.) 

•  From  Curve  IV.  it  appears  as  though  there  were  35  or  37  ripples  per 
period.  It  may  be  pointed  out  that  the  armatures  of  these  rotaries  are 
six-polar,  and  have  108  slots,  this  apparently  corresponding  to  the  number  of 
ripples  in  the  oscillogram. 


19(».]  RESONANCE   IN   ELECTRIC   CIRCUITS.  668 

The  process  of  parallelling  could  be  watched  on  the  oscillograph 
screen,  and  a  most  fascinating  sight  it  is  to  watch  the  D.C.  voltage 
spring  from  the  straight  line  to  a  wave  with  ripples  along  the  whole 
length,  and  then  to  see  the  main  wave  instantaneously  straighten  out, 
the  ripples  only  remaining  as  the  rotary  is  pulled  into  the  correct 
phase.  The  instantaneous  formation  of  the  ripples  on  the  A.C.  curve 
can  in  like  manner  be  watched. 

It  was  easy,  however,  to  ciemonstrate  the.  existence  of  the  D.C.  ripples 
independently  of  the  oscillograph,  and  for  this  purpose  I  drdve  one 
rotary  by  an  independent  motor  as  a  D.C.  generator,  and  a  second 
rotary  parallel  with  the  power-station  in  the  usual  way.  The  two  + 
brushes  were  connected  together,  and  the  negative  brushes  through  a 
hot-wire  voltmeter  in  parallel  with  a  Weston.  The  excitation  was 
adjusted  till  the  latter  voltmeter  read  zero  ;  the  hot-wire  instrument 
on  the  other  hand  indicated  12  volts.  The  latter  instrument  was,  of 
course,  merely  measuring  the  square  root  of  the  mean  square  of  the 
ripple. 

This  corresponds  to  a  total  fluctuation  from  crest  to  hollow  of 
34  volts,  or,  say,  under  normal  running  conditionSf  6*8.  I  have  tried  to 
filter  out  the  alternating  component 
of  the  D.C.  voltage,  and  transform  it 
up,  by  passing  it  round  one  winding 
of  a  static  transformer,  neutralising 
the  magnetic  saturation  created  by 
the  D.C.  component  by  a  current  from 
a  battery,  but  I  have  not  succeeded 
in  doing  it.  Curve  IV.— E.M.F.  Curve  of 

If  I  could  have   borrowed  a  500-  Rotary  as  A.C.  Generator, 

volt  accumulator  battery  in  order  to 

oppose  it  to  the  D.C.  voltage  of  the  rotary,  I  think  I  could  have 
obtained  a  considerable  300-cycle  current  through  the  battery.  As  I 
shall  show  afterwards,  I  am  able  to  accentuate  these  D.C.  ripples 
considerably  under  special  circumstances. 

I  further  observed  the  current  flowing  into  the  D.C.  feeder  circuits 
of  the  tramway  system,  but  could  find  practically  no  trace  of  a  ripple 
at  all.  The  loss  in  outside  circuits  due  to  the  ripple  was  therefore 
negligible. 

If  we  took  the  square  root  of  mean  square  of  the  voltage  ripple  as 
3  per  cent,  of  500  volts,  and  the  current  ripple  in  proportion,  viz.,  3  per 
cent.,  and  if  we  assumed  that  the  whole  of  the  A.C.  component  was 
wasted  in  heat,  ii  would  represent  merely  9  units  in  10,000.  I  am 
therefore  justified  in  saying  that  under  normal  conditions  the  loss  due 
to  the  D.C.  ripple  does  not  amount  to  i  per  mil. 

There  is  no  doubt  that  the  source  of  these  ripples  lies  in  the  teeth 
of  the  generators,  there  being  12  teeth  per  period  and  12  ripples  per 
cycle  superimposed  on  the  D.C.  voltage.  The  ripples  exist  in  the 
high-tension  voltage,  pass  through  the  transformers,  through  the 
rotaries  to  the  D.C.  side,  and  if  other  rotaries  be  run  as  motors  from 
the  D.C.  'bus-bar,  the  ripples  reappear  at  the  A.C.  slip-rings.  It  seems 
impossible  to  get  rid  of  them  by  filtering  them  out.    We  have  already 


654        FIELD  :  A  STUDY   OF  THE   PHENOMENON   OF      [Glasgow, 


disposed  of  the  suggestion  that  they  originate  in  the  rotarics  them- 
selves. I  think  no  one  will  venture  to  assert  that  the  transformers 
manufacture  them.  One  way  to  decide  that  point  would  be  to  connect 
the  oscillograph  direct  in  the  high-tension  circuit ;  although  I  have  not 
done  this,  I  have  another  proof  (although  to  my  mind  no  proof  is 
necessary),  and  that  is,  when  one  generator  only  is  running  in  the 
power-house  the  ripples  are  always  present,  though  somewhat  waver- 
ing at  times — when  two  generators  are  runrflng  in  parallel  the  ripples 
often  alternately  appear  and  disappear  with  a  regular  periodicity 
lasting  several  seconds.    This  is  evidently  due  to  the  swinging  of  one 


Curve  V.— Current  and  E.M.F.  of 
Rotary  on  no  load,  under-excited. 
Lagging  current  into  rotary  =  650 
amps. 


Curve  VI. — Same  as  V.,  but  over- 
excited. Leading  current  into  rotary 
=  600  amps. 


Curve  Vll.—Current  and  E.M.F.  of  Rotary 
on  normal  traction  load,  in  parallel  with  two 
others. 


Curve  VIII.— Current  and  E.M.F. 
of  Rotary  on  normal  traction  load, 
in  parallel  with  one  other. 


Curve  IX.— E.M.F.  and  Current  of 
Rotary  on  no  load,  excitation  ad- 
justed to  give  minimum  armature 
current. 


generator  relatively  to  the  other ;  when  exactly  in  phase  the  ripples 
appear,  when  displaced  by  half  the  wave  length  of  the  ripple  they 
practically  disappear.  The  same  thing  happens  with  the  ripples 
in  the  A.C.  voltage.  I  have  seen  an  almost  rounded  A.C.  voltage 
curve  suddenly  jump  into  peaks  as  one  generator  was  switched  out  of 
parallel. 

Granting,  then,  that  the  generator  E.M.F.  wave  possesses  high 
harmonics,  and  the  back  E.M.F.  of  the  rotaries  is  a  smooth  wave  (as 
indeed  one  would  expect  from  such  a  type  of  armature,  and  as  is 
shown  to  be  the  case  in  Curve  IV.),  it  is  evident  that  the  rotary  can 
supply  no  back  E.M.F.  to  equilibriate  the  ripples  of  the  applied  E.M.F. 
What  must  happen  in  such  a  case  is  that  when  the  opposing  E.M.F.'s 
do  not  balance  owing  to  a  ripple  in  the  one  and  not  in  the  other,  a 


1903,] 


RESONANCE   IN   ELECTRIC   CIRCUITS. 


655 


wattless — which  I  afterwards  call  a  self-induction — current  must  rush 
in  or  out  of  the  rotary,  which  will  absorb  or  equilibriate  the  difference 
of  voltage.  Curves  V.  to  IX.  show  this  clearly.  In  the  latter  case  the 
rotary  was  running  unloaded  under  condition  of  minimum  armature 
current.  It  will  be  seen  that  the  amplitude  of  the  ripples  of  the 
current  waves  seems  larger  than  that  of  the  main  wave  itself,  the  latter 
being  scarcely  distinguishable. 

It  is  interesting  to  note  that  the  current  wave  is  rippled  more 
uniformly  than  the  voltage  wave. 

The  main  drift  of  the  first  portion  of  this  paper  is  to  discuss  the 
conditions  under  which  resonance  may  occur  with  one  of  the  higher 
harmonics  of  the  E.M.F.  wave  introduced  by  the  particular  form  of 
toothed  armature  in  use  at  the  power-station.  Let  us  first  examine  the 
construction  of  the  armature.  Fig.  6  is  reproduced  from  a  scale 
drawing  of  the  armature  slots,  and  field  magnet  pole-shoes.  From  an 
examination  of  this  figure  it  will  be  obvious  that  the  magnetic  flux  must 


niuinnj 


lJ    Li    U    Lj 


Fig.  6. 


be  constantly  shifting  backwards  and  forwards  along  the  pole-face  as 
tooth  by  tooth  of  the  armature  is  passed.  It  does  not  necessarily  mean 
that  the  total  flux  through  the  field  system  fluctuates,  but  that  this  flux 
emerges  from  the  pole-face  in  "tufts"  opposite  the  armature  teeth, 
and  that  these  tufts  of  magnetism  are  dragged  backwards,  and  spring 
forwards  along  the  pole-face  according  as  the  magnetic  reluctance  is 
charged  at  different  parts  of  the  same  by  the  change  of  position 
relative  to  the  armature  teeth.  The  poles  are  champfered  off  so  as  to 
avoid  as  far  as  possible  change  of  total  flux  through  the  field  system. 
I  do  not  think  this  goes  on  to  any  marked  extent ;  it  would  be  possible 
to  detect  such  periodic  changes  by  looking  for  fluctuations  of  exciting 
current  This  could  be  done  by  suitably  inserting  the  oscillograph  in 
the  exciter  circuit.*  On  the  other  hand,  an  examination  of  Fig.  6 
would  lead  us  to  expect  six  more  or  less  sudden  irregularities  or 
excrescences  per  half-wave  of  the  curve  representing  total  threading 
of  magnetic  fluxf  by  the  armature  coils.    This  does  not  mean  a  12th 

•  I  have  tried  this  experiment  under  difficulties,  and  certainly  detected 
slight  and  rapid  periodic  fluctuations  in  the  exciting  current.  The  experi- 
ment is  well  worth  repeating,  however,  my  results  being  by  no  means 
conclusive. 

t  By  threading  of  magnetic  flux  I  wish  to  indicate  the  sum  total  of  mag- 
netic flux  interlinked  with  each  turn  of  the  armature  winding. 


666       FIELD:  A  STUDY   OF  THE   PHENOMENON  OF     [Glasgow, 

harmonic ;  afi  even  harmonic  would  be  impossible  with  such  a 
generator— it  would  mean  that  the  positive  half -wave  was  of  a  diflEerent 
shape  from  the  negative  half,  and  the  right-hand  half  of  each  half -wave 
was  of  a  different  shape  from  the  left-hand  half.  This,  of  course,  with 
such  a  generator  is  impossible.* 

If,  however,  we  consider  a  smooth  wave  (not  necessarily  a  sine  wave) 
with  6  ripples  per  half-period  superimposed  in  the  manner  indicated 
in  Fig.  6a  so  that  the  ripples  are  wholly  positive  during  the  positive 
half-period  and  wholly  negative  during  the  negative  half-period,  we 


Fig.  6a, 


should  get  a  curve  such  as  we  might  reasonably  expect  with  a  12  slot 
per  period  alternator.  This  curve  of  total  threading  of  magnetic  flux 
would  be  quite  symmetrical,  and  would  possess  12  irregularities  cor- 
responding to  the  number  of  teeth. 

It  is  therefore  instructive  to  study  this  case,  and  to  simplify  matters 
we  will  assume  that  the  ripple  between  0  and  v  can  be  represented  as 

•  In  making  this  statement  I  am  leaving  out  of  account  all  extraneous 
effects,  such  as  hysteresis  in  the  armature  teeth,  cross  magnetisation,  etc. 
Later  on  we  fincf  curves  in  which  the  right  and  left  halves  are  different 
owing  to  some  such  effects,  in  all  probability.  I  mean  here  that,  provided 
the  winding,  slots,  pole-pieces,  etc.,  are  symmetrical,  the  process  of  the  flux 
cutting  into  an  armature  coil  must  be  the  exact  reverse  of  cutting  out  of  a 
coil  ;  moreover,  the  flux  from  an  S-poIe  must  of  necessity  cut  in  and  out  in 
the  exact  manner  as  does  the  flux  from  the  N-pole. 


1903.]  '  RESONANCE    IN   ELECTRIC  CIRCUITS.  657 

a  (i  —  cos  12  k  t)  and  between  «-  and  2  ir  as  —  a  (i  —  cos  12  )fe  /)•  The 
fundamental  term  is  F  N  sin  *  /  (F  N  being  the  maximum  interlinkage 
of  flux  with  armature  winding). 

Now,  we  can  quite  easily  split  this  up  into  a  Fourier's  series ;  the 
amplitude  of  the  p^  sine  term  will  be  proportional  to  *— 

/x  (^)  -/x  (0), 

and  of  the  p^  cosine  term  to — 

Where/,  {k  i)  represents — 

fci  -cosi2^/)sin/A/  rf/or-  i,  cospki-\-  cos  (^  +  12)^/  ^ 
J  pk  2  i^p  -\'  12)  k 

cos  (p  —  12)  kt 

~~2XP  —  12)  *      * 

and  /a  (^  /)  represents — 

I  (i  —  cos  12  kt)  cos  ^)fe/  <//  or -?-  sin /> * /  -  5L"iA±J2)_^^  + 
J  pk       "^  2   p  —  12)  k 

sin  (^  —  12)  AJ  • 
2  (/►  —  12)  k 

If  ^  is  even,  cos  (^  ±  12)  x  =  +  i. 

If  p  is  odd,  cos  ()^  ±  12)  IT  ==  —  I. 

If  p  is  odd  or  even,  sin  (^  ±  12)  ir  =  o. 

.  • .  /,  (x)  — /,  (0)  oc  (^  —  V,  ^    ^  where  ^  is  odd, 

^«  (t)  — /,  (<?)  =  0  „  even, 

4  («•)  —/a  (0)  =  0  „  odd  or  even. 

This  shows  us  that  in  this  expansion  the  odd  harmonics  only  enter 
in,  and  they  are  all  sine  terms. 

Now,  ^//xa  _  j^\  becomes  infinite  when  /  =  12,  as  />  can  only 
have  odd  integral  values  we  see  that  the  nth  and  13th  harmonics  are 
the  most  important. 

The  relative  amplitudes  of  the  harmonics  in  the  expression  for 
E.M.F.  are  obtained  from  those  representing  total  interlinkage  of  flux 
by  multiplying  by  the  corresponding  order  of  harmonic.  This  has 
been  represented  in  the  following  table  : — 


Flux. 

E.M.F. 

7th  Harmonic,  |  +   t,'^  =       -215 

150 

9th 

4  +  A  =      -253 

227 

nth 

T»T  H-    U    =          -568 

6-24 

13th 

Vj—  i'5  =-'444 

-577 

15th 

tV-  «  =-119 

-178 

17th 

Vt  —  ^:i\  =  —  -059 

—  i-oo 

•  The  full  expression  is,  of  course — 
{/.  M  -  /i  W  }  +  I  -/i  (2  tt)  +/,  (x)  I  which  in  our  case  is  2  If,  (tt)  -/,  (0)]. 


668        FIELD  :  A   STUDY  OF  THE   PHENOMENON   OF     [Glasgow, 

We  may  say  generally  that  the  most  important  harmonics  where 
there  arc  q  teeth  in  the  generator  per  pair  of  poles  are  the 

{q—  i)«  and  the  (^  H-  i)^ 

unless  indeed  the  grouping  of  the  armature  conductors  is  such  as 
would  naturally  introduce  other  harmonics  of  important  magnitude, 
independent  of  whether  the  armature  be  smooth  or  not. 

The  question  now  arises  whether  12  ripples  in  the  D.C.  voltage  per 
cycle  are  consistent  with  an  nth  and  13th  harmonic.  I  think  so.  If 
we  consider  the  13th  harmonic  occurring  similarly  in  the  three  phases, 
A,  B,  C,  then  the  harmonic  in  phase  B  will  be  120  deg.  of  its  own 
period  in  advance  of  the  harmonic  in  A.  Similarly  the  harmonic  in  C 
will  be  in  advance  of  that  in  B  by  120  deg.  This  means  that  we  have 
a  true  "  three-phase  ripple "  advancing  in  the  same  direction  as  the 
main  wave,  but  with  13  times  the  velocity.  Now,  look  at  the  nth 
harmonic ;  in  phase  B  it  will  be  2/3  period  in  advance  of  that  in  A  ; 
similarly  C  will  be  2/3  period  in  advance  of  B.  This,  again,  will  form 
a  "three-phase  ripple,"  but  retreating  this  time  w|th  11  times  the 
velocity  of  the  main  wave.  What  does  this  mean  in  the  rotary 
converter  ?  The  armature  is  rotating,  say,  at  n  revolutions  forwards  ; 
the  three-phase  current  in  it  produces  a  backward  rotating  field  of 
speed  n  relative  to  the  armature,  or  at  rest  relativel}'  to  the  field  s)rstem. 
The  13th  harmonic,  travelling  13  times  as  fast  and  in  the  same 
direction,  corresponds  to  a  rotating  field  revolving  at  a  speed  of 
(13  —  i)  times  that  of  the  armature  relative  to  the  fixed  position  of  the 
brushes,  while  the  nth  harmonic  produces  a  field  rotating  in  the 
opposite  direction,  and  therefore  with  (11  -f  i)  times  the  speed  of  the 
armature  relatively  to  the  fixed  frame  of  the  rotary. 

Both  of  these  harmonics  will  therefore  have  the  effect  of  producing 
12  ripples  per  cycle  in  the  D.C.  voltage.  The  same  argument  could 
not  be  applied  to  the  17th,  19th,  or  any  other  harmonics ;  if,  therefore, 
for  any  reason  these  predominate,  we  should  expect  the  D.C.  voltage 
line  to  be  somewhat  broken  and  jagged.  In  this  connection  refer  to 
Curves  X  and  XII,  and  compare  also  the  undulating  voltages. 

Again,  if  we  assume  that  (due  to  the  changing  magnetic  reluctance 
of  the  circuit  as  the  pole  assumes  different  positions  relatively  to  the 
armature  teeth)  fluctuations  in  the  total  magnetism  emerging  from  the 
polar  surface  are  introduced,  we  can  imagine  that  the  field  system  is 
giving  a  rise  to  a  constant,  plus  an  alternating,  flux.  This  alternating 
flux  will  have  a  frequency  of  q  where  PU  equals  the  frequency  of  the 
generator.  This  alternating  flux  is,  moreover,  equivalent  to  two 
rotating  fluxes  rotating  forwards  and  backwards  with  q  times  the 
velocity  of  the  field  system.  If  we  add  the  rotation  of  the  field  system, 
we  have  a  main  or  fundamental  field  rotating  at,  say,  unit  speed,  a 
forward  rotating  field  at  9  +  i,  and  a  backward  rotating  field  at  a 
speed  of  ^  —  i.  Hence  variation  of  total  flux  will  likewise  give  rise  to 
the  nth  and  13th  harmonics. 

We  now  come  to  the  question  of  1  the  magnification  or  accentuation 
of  the  harmonics.  This  can  be  brought  about,  in  my  opinion,  in  two 
entirely  distinct  and  separate  ways  : — 


1903.] 


RESONANCE   IN   ELECTRIC  CIRCUITS. 


659 


(i)  By  strongly  magnetising  the  tcetli  in  the  armature  by  the 

armature  currents  themselves; 
(2)  By  resonance,  pure  and  simple. 
These  two  causes  produce  results  of  a  very  similar  nature,  but  each 
phenomenon  appears  to  require  a  totally  different  explanation. 


AAAAAAAAAAAAAAA/W 

Curve  X.— A.C.  and  D.C.  E.M.F. 
of  Rotary.  Generator  supplying  140 
amps.,  lagging  current. 


Curve  XII.  — A.C.  and  D.C. 
E.M.F.'s.  One  rotary  running  with 
normal  excitation,  93,700  yards  of 
cable  connected. 


Curve  XIV.— Rotaries  on  no  load 
nver^excited,  185  amps.,  leading  at 
power-station. 


\AAAAAAAAAAAAAAAA/N 

Curve  XL— A.C.  and  D.C.  E.M.F. 
of  Rotary.  Generator  supplying  25 
amps.,  7  rotaries  running  on  no  load, 
normal  excitation,  93,700  yards  of 
cable  connected. 


Curve  XIII. — Rotaries  on  no  load, 
under-excited,  195  amps.,  lagging  at 
power  station. 


Curve    XV.  — E.M.F.    Wave    of 

Generator  on  no  load,  cables  adjusted 
for  partial  resonance  with  13th  har- 
monic. 


Examine  Curves  XI I L,  XIV.,  XV.  In  the  first  case,  a  lagging 
current,'  nearly  equal  in  amount  to  the  full -load  current  of  the 
generator,  was  being  given  out. 

Now,  a  lagging  current  involves  a  very  strongly-excited  field  system 
in  the  generator.  The  armature  current  will  be  of  a  demagnetising 
order,  and  will  produc     its  maximum  effect  when  the  pole  is  in  the 


660        FIELD  :  A  STUDY   OF  THE   PHENOMENON  OF     [Glasgow^, 

most  favourable  position  for  the  magnetisation  of  the  teeth  within 
the  coil. 

A  leading  current,  on  the  other  hand,  involves  a  weakly-excited 
field  system,  the  armature  currents  augmenting  the  magnetism  due  to 
the  field  winding  ;  again  the  pole  is  in  a  favourable  position  for  the 
magnetisation  of  the  teeth  by  the  armature  currents. 

It  appears,  curiously  enough,  that  the  lagging  current  produces  the 
greater  magnification  of  the  harmonics,  but  that  practically  the  full- 
load  current  is  necessary  to  produce  this  effect  to  any  great  extent. 
Turn  now  to  Curve  XV.  A  few  cables  only  were  in  circuit,  and  the 
current  flowing  out  of  the  generator  was  too  small  to  be  read  on  the 
station  instruments.    This  was  a  case  of  resonance. 

I  would  here  ask  pardon  for  digressing  into  the  elementary  theory 
of  electrical  resonance  for  the  benefit  of  any  present  who  may  not 
have  had  occasion  to  consider  the  subject. 


F^G.  7. 

The  current  flowing  into  a  condenser  may  be  expressed  in  effective 
amperes  bv 

2irnKV (7) 

where  n  =  frequency  of  the  circuit ; 

„    K  =  capacity  of  condenser  in  farads ; 

„    V  =  effective  volts. 

Again,  if  L  be  the  coefficient  of  self-induction  of  a  coil,  the  current 
passing  through  it  will  be  expressed  by 


(8) 


2  7rnL 
V  being  the  effective  volts  at  its  terminals. 

If  we  equate  (7)  and  (8)  we  get  the  condition  under  which  the 
capacity  current  equals  the  self-induction  current,  V  being  the  same  in 
each  case.    This  condition  is 


(2  7rnY  = 


LK 


(9) 


Let  us  suppose  that  we  have  a  pure  self-induction  and  a  pure  capacity 
connected  in  parallel,  as  in  Fig.  7. 

Let  the  alternating  E.M.F.  V  be  represented  by  the  vector  O  V ;  we 
know  that  the  capacity  current  will  be  90  deg.  in  advance  of  O  V,  that  is 


1903.] 


RESONANCE   IN   ELECTRIC   CIRCUITS. 


661 


in  position  OK;  we  also  know  that  current  flowing  through  the  self- 
induction  will  lag  behind  O  V  by  90  deg.    This  is  represented  by  O  L. 

If  now  equation  (9)  holds,  O  K  =  O  L,  and  the  resultant  of  these 
currents  as  far  as  the  outside  circuit  is  concerned,  is  zero  at  every 
instant.  We  have  then  the  case  of  a  combination,  of  which  the 
terminals  are  a  and  b  ;  when  this  combination  forms  part  of  a  closed 
circuit  in  which  an  alternating  E.M.F.,  of  frequency  n  and  value  v, 
is  generated,  no  ciurent  circulates  on  the  outside  circuit  act,  and 
the  potential  difference  between  a  and  b  is  V.  These  are  the  conditions 
which  would  hold  if  the  combination  were  removed  and  a  perfect 
insulator  substituted.  We  may  therefore  say  that  this  combination 
at  this  particular  frequency  behaves,  as  far  as  the  outside  circuit  is  con- 
cerned, as  a  perfect  insulator. 

Now,  introduce  resistance  r  into  each  arm  of  the  combination , 
and  modify  the  diagram  to  suit,  Fig.  8. 


O  L  and  O  K  will  not  now  lag  and  lead  by  quite  90  deg. ;  in  each  case 
we  have  an  ohmic  drop  O  r  in  phase  with  the  current,  and  an  E.M.F. 
O  /,  O  )fe  at  right  angles,  such  that  the  resultant  with  the  corresponding 
ohmic  drop  is  O  V. 

The  current  in  the  outside  circuit  will  be  O^,  which  is  equal  to 

0L« 


2  X  O  L  sin  X  ;  or  2  r 


OV 


and  will  be  in  phase  with  OV.     The    combination  therefore  will 
behave  as  though  it  had  an  ohmic  resistance  of 

P-Y!        i_' 
OL'  ^  2/' 

Now,OV=0/»-f  O;-';  O /«  =  (2x»L)' O  L»,  and  from  (8)  and 

{9)  we  can  write     ?-  for  4  iH*  w*, 

hence  O  V«  =  (t  -h  f)  O  L»  .W.  the  resistance  is  JL  +  - . 
K         '     '  2  Kr        2 


66-2         FIELD  :  A  STUDY   OF  THE   PHENOMENON   OF    [Glasgow. 

Let  us  take  an  example  and  put  L  =  i  secohm,  K  =  i  microfarad, 
r  =  I  ohm,  then  the  resistance  of  the  combination  will  be  0*5  megohm  ; 
thus  we  see  that  if  the  capacity  and  self-induction  be  not  pure,  but 
contain  also  a  small  amount  of  ohmic  resistance,  the  combination 
behaves  towards  the  outside  circuit  at  the  particular  frequency  as 
an  imperfect  insulator,  but  nevertheless  of  high  insulation  resistance. 
If  in  this  particular  case  we  make  the  further  condition  that 

-4;^  +  -  =  rorthatK=^, 

the  combination  is  equivalent  to  an  effective  resistance  of  r  ohms,  and 
this  will  as  a  matter  of  fact  be  true  not  only  for  sine  waves  of  the  one 
particular  frequency,  but  universally  for  any  periodic  or  unperiodic 
function  which  expresses  the  change  of  V  ;  in  fact,  under  these 
circumstances  the  current  in  the  outside  circuit  is  always  V/r. 

We  have  now  to  consider  a  perfect  self-induction  in  series  with 
a  perfect  capacity,  and  the  same  current  C  passing  through  each.  This 
modifies  the  diagram  shown  in  Fig.  7  somewhat. 

If  we  turn  O  L  through  90  deg.  forward,  the  E.M.F.  required 
to  overcome  self-induction  will  be  O  Vl  ;  if  we  turn  O  K  back  through 

g/  00(100  WOOWOOWOOOO  ^^^— qi^bi ,  ^^ 


■e 


e 

Fu;.  9. 

90  deg.  to  concide  with  O  L,  the  voltage  vector  will  take  the  position 
O  Vk  ;  see  Fig.  9. 

This  diagram  represents  the  state  of  things  when  the  same  current 
flows  through  capacity  and  self-induction,  and  the  current  is  at  its 
maximum. 

If,  therefore,  the  current  is  C,  and  is  represented  by  the  vector  O  L 
and  O  K,  the  potential  difference  between  a  and  d  will  be  the  vector 
O  Vl  and  between  d  and  b  the  vector  O  V^  ;  therefore  between  a  and  h 
the  potential  difference  will  be  the  sum  of  O  V^  and  O  V,. ,  which  is  at 
every  instant  zero.  We  are  therefore  sending  a  definite  current  through 
the  combination,  although  no  potential  difference  between  the  terminals 
a  and  h  is  necessary.  The  combination,  therefore,  behaves,  as  far 
as  the  outside  circuit  is  concerned,  at  this  particular  frequency  as 
a  perfect  conductor.  I  am  indebted  to  Mr.  R.  C.  Clinker  for  the 
notion  of  a  perfect  insulator  and  perfect  conductor  here  introduced. 
The  current  strength  in  the  circuit  acb  will  be  determined  by  the 
resistance  of  this  portion  of  the  circuit  and  the  E.M.F.  induced  in  it. 
If  the  resistance  be  low,  the  current  will  rise  to  a  correspondingly 
high  figure. 


1903.] 


RESONANCE   IN  ELECTRIC  CIRCUITS. 


663 


Now,  although  the  potential  di£Ference  between  a  and  b  is  zero,  we 
know  that  that  between  a  and  dord  and  b  is  given  by  equations  (7)  and 
(8).  Let  us  therefore  imagine  the  E.M.F.  E  acting  in  the  circuit,  the 
self-induction  short-circuited,  and  the  current  measured  to  be  c  ;  then, 
if  the  capacity  be  short-circuited  instead  of  the  selfrinduction,  we  shall 
have  again  the  current  c  flowing. 

If  both  be  short-circuited  we  shall  have  a  current  of  E/p  where  p  = 
resistance  of  portion  acb.  Now,  E/p  may  be  10, 100,  1000,  etc.,  times  c, 
just  depending  on  the  value  of  p.  But  if  both  self-induction  and 
capacity  remain  unshort-circuited,  the  same  current  will  flow  as  if 
short-circuited  :  hence,  in  the  former  case  the  potential  difference  a  d 
or  ab  will  be  approximately  10,  100,  1000  times  E,  as  the  case 
may  be,  just  depending  on  the  ratio  of  E/p  to  c.  This  is  what  is  known 
as  electrical  resonance,  when  the  combination  of  self-induction  and 
capacity  acts  like  a  perfect  conductor,  or  a  nearly  perfect  conductor, 
as  far  as  the  outside  circuit  is  concerned,  there  being,  however,  a  rise 

of  potential  within  the  combination  equal  to  C  \/ ^ . 

Of  course,  if  we  consider  the  self-induction  as  possessing  resistance  r, 


Fig.  id. 


and  the  capacity  also  the  same  resistance,  the  combination  will 
behave  as  an  imperfect  conductor  with  ohmic  resistance  2  r  ohms,  i.e., 
the  potential  difference  between  a  and  6  will  be  2rC  and  in  phase 
with  C. 

In  alternating  electric  supply  circuits  we  often  have  to  deal  with  self- 
inductions  and  capacities  which  would  check  the  current  down  to  the 
same  values  if  the  same  E.M.F.  were  applied  to  each,  which  is 
the  necessary  condition  for  resonance  ;  consider,  for  example,  a  two- 
phase  cable  with  two  insulated  cores  within  a  common  outer  as  return  ; 
see  Fig.  10. 

Suppose  phase  B  in  the  power-house  has  been  opened,  and  consider 
the  state  of  things  that  exists ;  we  can  represent  it  as  shown  in  Fig.  1 1. 
Current  enters  conductor  a,  and  returns  by  conductor  c ;  it  can 
flow  through  the  capacity  a  c,  and  the  self-induction  a  c,  these  being  in 
parallel ;  but  an  alternative  path  is  through  capacity  a  b,  and  thence 
through  capacity  6c  in  parallel  with  self-induction  be. 

Suppose  the  frequency  is  25,  the  voltage  per  phase  =  3000  volts,  the 

.transformers  at  the  end  of  the  line  150  kw.  each,  and  such  as  to 

take  a  magnetising  current  of  2  per  cent,  of  full-load  current  or 

one  ampere  ;  secondary  circuits  are  open.     Let  the  capacity  between 

either  conductor  a  or  b  and  sheath,  the  other  conductor  being  grounded 

Vol.  82.  44 


664        FIELD  :  A  STUDY  OF  THE   PHENOMENON  OF    [Glasgow, 

be  75  mf .  per  mile,  and  between  a  and  b  together,  and  sheath  '9  mf . 
per  mile,  i.e,  cap :  (a  +  c),  6  =  75,  and  cap :  (a  +  ^),  c  =  'g  mf . 
per  mile,  then  we  have  a  capacity  effect  equivalent  to  that  shown 
in  Fig  II.  Let  the  length  of  line  be  2*83  miles,  then  the  total  capacity 
a  c,  =  1*27  mf.  and  total  capacity  a  6,  =s  -847  mf.  If.  now  the  potential 
difference  between  b  and  c  is  V,,  the  current  through  the  transformer 
6 c  is  ^»/3ooo  =  .3*33  X  ^^~^  V„  and  through  the  capacity  be,  2  x 
10-^  V,.    The  current  arriving  at  6  will  therefore  be  a  wattless  current. 


lagging  90  deg.  between  the  E.M.F.  and  equal  to  133  io-<  V,.  But  if 
the  difference  of  potential  between  a  and  b  is  V„  we  have  again  a 
capacity  current  through  a  6  of  1*33  10-^  V,. 

Thus  we  have  the  necessary  conditions  for  resonance,  and  the 
potential  of  the  switched-out  conductor  b  will  rise  until  the  insulation 
somewhere  in  the  cable  gives  way  and  modifies  the  conditions.  This 
has  merely  been  given  as  an  example ;  there  are,  of  course,  a  large 
number  of  combinations  possible  where  resonance  might  occur,  and 


m 


smmmmu 


m 


Fig.  12. 


every  station  engineer  is  more  or  less  on  the  alert  for  them.  A  most 
interesting  paper  on  the  subject  of  high-tension  cable  breakdowns  from 
resonance  effects  appeared  in  the  •*  Electrotechnische  Zeitschrif t "  on 
28th  December,  1899,  by  Mr.  Gisbert  Kapp,  and  was  translated  by  the 
present  writer  for  the  Electrical  Rrview,  and  appeared  in  the  9th  and 
23rd  March  issues  of  that  paper  in  1900. 

Now,  every  alternator  possesses  reaction  and  self-induction.  By 
reaction  I  usually  mean  that  the  armature  currents  produce  magnetic 
lines  which  thread  through  the  magnetic  path  in  the  field  system, 
either  weaHening  or  strengthening  it,  according  as  the  armature 
ampere- turns  assist  or  oppose  the  field  system  magnetising  force.  The 
term  self-induction  I  usually  apply  to  those  lines  of  force  generated  by 


1903.]  RESONANCE   IN    ELECTRIC   CIRCUITS.  G65 

the  armature  currents  whigh  do  not  produce  an  alteration  of  the  total 
flux  in  the  field  system,  but  which  close  round  the  armature  windings 
without  including  the  field-magnet  windings.  Both  of  these  effects  are 
more  or  less  proportioned  to  the  strength  of  the  armature  currents,  and 
result  in  an  alteration  of  the  magnetism  threading  the  armature 
windings.  This  diminution  or  increase,  as  the  case  may  be,  induces  an 
E.M.F.  in  quadrature  with  the  current,  and  may  therefore  be  looked 
upon  as  a  self-induction. 

Every  alternator,  therefore,  may  be  represented  by  an  imaginary 
machine  producing  an  alternating  E.M.F.,  without  self-induction  and 
without  reaction,  but  with  a  choking  coil  in  series  with  it.  Un- 
fortunately, as  we  shall  see  later,  it  is  necessary  to  consider  the 
choking  coil  as  having  a  variable  coefficient  of  self-induction,  which  is 
however,  a  periodic  function  of  time.  We  may  thus  represent  a  three- 
phase  alternator  connected  to  a  cable  as  in  Fig.  12. 


Fig.  13a.  Fig.  136.  Fig.  13c. 

In  talking  of  the  self-induction  of  an  alternator,  I  shall  for  the 
purpose  of  this  paper  include  in  the  term  the  armature  reaction,  ue.,  I 
shall  refer  to  that  self-induction  (whether  with  constant  or  variable 
coefficient)  which  inserted  in  spries  with  a  reactionlcss  and  self- 
inductionless  machine  would  give  the  same  characteristics. 

The  capacity  of  a  three-phase  three-core  lead-sheathed  cable  may 
be  considered  as  a  combination  of  capacities,  as  in  Fig.  13  (a).* 

A  three-phase  A  capacity  as  shown  in  Fig.  13  (6)  will  take  the  same 

current  per  line  wire  as  a  Y  capacity  as  in  Fig.  13  (c)  if  K  =     . 

3 
We  do  not  in   practice  meet    cases   where  the   self-induction   of 

•  We  are  justified  in  assuming  the  capacity  effect  of  a  multiple  core  lead- 
sheathed  cable  can  be  exactly  represented  by  actual  capacities  between  the 
individual  conductors,  and  between  the  conductors  and  lead  sheath,  for 
taking  the  case  of  a  three-core  cable,  we  know  that  if  Q,  Q^.  Q„  V,  V^  V, 
represent  the  charges  and  potentials  of  the  various  conductors,  the  lead 
bheath  being  grounded,  we  have  the  relations— 

Qi  =  fl...  V,  +  a,.,  V,  +  <i.-5  V3 (10) 

and  similarly  for  Q,  and  Q3,  where  the  a  coefficients  are  constants  of  the 
same  dimensions  as  capacity. 

Now,  if  we  consider  capacities  K„  K,.,j  K,^  connected  between  the  con- 


/ 


666        FIELD:  A  STUDY   OF  THE   PHENOMENON   OF     [Glasgow, 

the  alternator  will  produce  resonance  with  the  capacity  of  the  cable 

system  at  the  fundamental  frequency.     For  example,  taking  a  large 

three-phase  cable  system  as  represented  by    a 

three-legged  capacity  of  5  mf .  per  leg,  the  capacity 

^^"'^  current  per  leg  at  6,500  volts  per  phase,  25  cycles 

^     -,— o4cr.         would  be  2*95  amperes.    Fig.  14. 

The  self-induction  in  the  alternator  which 
I        ^,xk^^  would  produce  resonance  with  this  cable  system 

^A^         /^^       would   therefore   be  such  as   would  only  allow 
2*95  amps,  per  leg  to  circulate  when  the  generator 
Fig.  14.  was  excited  to  6,500  volts,  and  short-circuited. 

Such   an    alternator    would    be    manifestly   in- 
adequate in  connection  with  such  a  cable  system,  but  might  perhaps 

ductors,  and  K,a  K,^  Kj^  connected  between  the  conductors  and  sheath,  wc 
have : — 

Q.  =  K,.,  (V,  -  V«)  +  K,.,  (V,  -  V3)  -f  K,^  V.     .    .    (II), 

and  similarly  with  Qa  and  Q3. 
This  can  be  written  as — 

Q,  =  (K,.,  H-  K,.3  +  K„)  V,  -  K,..  V,  -  K,.3  V3. 

Hence       a,.,  =  Ki.a  +  K,.3  -|-  K,^ 

-  a,.,  =  K,.a 

-  <i,.3  =  Ki.j ,  and  so  on. 

We  therefore  see  that  (11)  is  only  another  way  of  writing  (10)  ;  if  then 
we  determine  K,.,  K,-3  K,^,  etc.,  by  experiment,  we  can  consider  these  as 
actual  capacities  connected  as  represented  by  eq.  (11). 

Owing  to  symmetry  in  a  three-core  cable  we  can  write — 

and    K,^  =  K,.3  =  Kj^  =  S. 

Now,  if  2  and  3  be  earthed,  we  have — 

Q,  =  (2  K  +  S)  V, (12). 

If  2  and  3  be  connected  together  but  not  earthed,  and  if  they  together 
have  an  equal  and  opposite  charge  to  that  on  i,  we  have — 

Q,  =  (2K-f-S)Vx  -  2KV. 

Q,  =  (K  +  S)  Va  -  KV,  =  -  2£ 

2 

.•      V,  =  -^J,andQ,  =  (2K  +  |S)(V,  -  V»)     .     .    .     (13). 

Lastly,  if  3  be  left  insulated  without  charge,  and  if  the  charge  on  2  t)e 
equal  and  opposite  to  that  on  i,  we  have — 

Q.  =  (2  K  +  S)  V.  -  K  (V,  +  V3) 
V    =  —  V 
and    o'  =  (2K  V  S)  V3  -  KV,  -  K V„  ix.,  V3  =  O. 

Qx  =  (3K  +  S)V.  =  gK  +  |)(v.  -  V,)    .    .    .     (14). 

If,  therefore,  we  measure  Q  and  the  P.D.  in  any  two  of  these  cases,  we 
have  all  particulars  necessary  tor  the  determination  of  the  capacity  constants 
of  the  cable,  and  can  treat  these  as  if  they  were  actual  capacities  connected 
as  shown  in  Fig.  13(a),  where  the  centre  point  is  the  lead  sheath. 

We  shall  have  occasion  to  make  use  of  (12),  (13),  and  (14),  a  little  later. 


This  gives 


1903.]  RESONANCE   IN   ELECTRIC  CIRCUITS.  667 

be  used  for  applying  a  pressure  test  to  the  cables,  in  which  case,  of 
course,  the  greatest  care  would  have  to  be  exercised. 

Although  the  self-induction  of  the  supply  alternator  will  not 
produce  resonance  at  the  fundamental  frequency,  it  does  not  at  all 
follow  that  such  may  not  occur,  due  to  a  higher  harmonic  of  the  E.M.F. 
The  current  which  a  given  capacity  will  take  at  a  given  voltage  is  pro- 
portional to  a  frequency,  while  the  current  which  a  self-induction  will 
pass  at  the  same  voltage  is  inversely  proportional  to  the  frequency. 

In  the  above  case  the  capacity  current  per  looo  volts  corresponding 
to  the  nth  harmonic  would  be  8*65  amps.  A  self-induction  which 
would  pass  8*65  amps,  at  1000  volts  275  cycles  per  second  would  pass 
356  amps,  at  3,750  volts  and  25  cycles,  or  an  alternator  with  this  self- 
induction  per  leg  would  give  on  short-circuit  356  amps,  per  leg  when 
excited  to  6,500  volts  per  phase.  (I  have  chosen  this  figure,  because  it 
nearly  corresponds  with  the  results  taken  from  the  2,500  kw.  generators 
in  Glasgow.)  We  should  therefore  at  first  sight  expect  to  obtain 
resonance  with  such  an  alternator,  and  a  cable  system  corresponding  to 
Fig.  14,  if  an  nth  harmonic  existed  in  the  E.M.F.  wave. 

I  made  some  experiments  to  determine  the  capacity  of  the  cables, 
by  inserting  a  hot-wire  ammeter  in  circuit,  but  I  obtained  strangely 
inconsistent  readings  ;  I  therefore  forbear  to  give  them. 

Mr.  R.  C.  Clinker  made  some  tests  on  similar  cables  for  the  Central 
London  Railway,  and  obtained  the  following  results  per  mile  : — 

1.  From  one  core  to  other  two  cores  -f  lead  sheath  =  '38  mf. 

2.  From  one  core  to  other  two  cores,  sheath  disconnected  and 
earthed  =  32  mf. 

3.  From  one  core  to  one  other  core,  3rd-core  insulated,  sheath 
disconnected  and  earthed  =  '23  mf . 

If  K  be  the  capacity  from  core  to  core,  and  S  the  capacity  from  core 
to  sheath,  and  assuming  the  insulation  of  both  poles  of  the  testing 
circuit  to  be  so  good  that  all  leakage  currents  were  negligible  in 
comparison  with  the  capacity  currents,  we  see  that  we  have  : — 

By  test  (i)  2  K  -h  S  =  -38 
„      (2)  2  K  +  ?  S  =  -32 
.-.  S  =  -i8  K  =  -i 

and  by  test  (3)  we  have  a  capacity  of 

2^  +  2 

Which  with  above  values  of  K  and  S  equals  '24  as  against  '23  actually 
measured. 

The  above  cable  is  therefore  equivalent  to  a  Y  capacity  of  '48 
mf.  per  leg  per  mile,  and  therefore  io'4  miles  would  give  the 
capacity  represented  in  Fig.  14. 

As  a  matter  of  fact,  I  find  considerably  more  cable  is  needed 
to  produce  resonance,  and  I  think  this  is  probably  due  to  the  fact 
that  the  coefficient  of  self-induction  of  the  alternator  is  by  no 
means  the  same  for  the  fundamental  as  for  the  higher  harmonics. 


GGS 


FIELD  :  A  STUDY  OK  THE    PHENOMENON   OF    [Glasgow. 


We  know  that  the  coefficient  of  self-induction  of  such  a  machine 
varies  between  wide  limits,  it  must  depend  on  the  relative  position 
of  field  system  to  armature  coils,  and  also  on  the  value  of  the 
armature  current  in  each  position.  Fig.  15  represents  what  is  known 
as  the  curve  of  synchronous  impedance  of  the  Glasgow  alternators ; 
or  the  short-circuit  armature  current,  in  terms  of  armature  volts 
on  open  circuit  with  the  same  field  excitation  at  synchronous 
speed. 

In  the  first  place,  it  is  clear  that  by  this  method  the  self-induction 
should  be  a  maximum,  since  the  poles  are  in  the  most  favourable 
position  when  the  armature  currents  are  at  their  maximum.  Next, 
we  see  that  even  this  method  does  not  give  a  constant  coefficient. 
If  we  take  the  area  of  one-half  period  of  the  E.M,F.  wave  as 
proportional  to  the  square  root  of  the  mean  square,  and  the  maximum 
of  the  current  as  proportional  to  the  R.M.S.,  which  would  be  correct 


*»^ 

i 

^ 

^ 

I 

y 

y' 

i 

/ 

/ 

— - 

z 

A 

/ 

1 

■/ 

/ 

— 

tfM 

9tfP\ 

V  i 

HTl 

QAH 

£C- 

TX  A 

ITMlif 

A 

— - 

"-"- 

• 

r . 

!f2 

• 

'Aa. 

mnt 

IC 

* 

U  '■ 

Fig.  15. 


assumptions  if  we  were  dealing  with  sine  functions,  then  the  volts 

would  be  proportional  to,  or  represent  maximum  flux,  and  current, 

the  maximum  current  producing  such  flux,  in  which  case  the  slope 

</N 
of  the  synchronous  impedance  curve  represents  -rp,  where  N  is  the 

total  flux  produced  by  the  current  C. 

Now  -r-7^  =  -Ti  '  j7^,  therefore  the  slope  which  we  will  call  tan  9 is 

such  that 


/>tan«_-=^-(orL_=EJ, 


which  means  that  tan  9  at  every  point  of  the  curve  is  proportional 
to  the  coefficient  of  self-induction  for  that  particular  current  strength. 

Fig.  15  shows  that  this  varies  between  the  limits  of  1*3  at  low 
currents  and  0-5  at  300  amperes. 

We  see  then  that  the  coefficient  of  self-induction  has  a  different 
value  for  each  ripple  on  the  E.M.F.   wave,   due   to  the  position  of 


1903.] 


RESONANCE   IN   ELECTRIC   CIRCUITS. 


the  field  system  ;  and,  again,  when  a  heavy  armature  current  is  being 
generated,  the  coefficient  is  further  modified  by  the  degree  of 
magnetic  saturation  of  the  armature.  The  resultant  of  these  two 
effects  must  depend  largely  on  the  power-factor  of  the  circuit,  and 
will  be  an  extremely  complicated  function  to  express. 

If  we  examine  Curves  XVI.  and  XVII.  we  see  that  with  93,700  yards 
of  cable  in  circuit  we  obtain  the  nth  harmonic  accentuated;  with 
somewhat  less  cable  in  I  have  obtained  resonance  due  to  the  nth 
harmonic,  but  could  not  obtain  a  photographic  record.  Curves  XVI. 
and  XVII.  were  taken  with  about  twelve  months'  interval.  The 
first  was  traced  by  hand ;  the  second  photographed.  I  cannot  vouch 
for  the  engine  speed  being  exactly  the  same  in  each  case.  On 
reducing  the  capacity  I  brought  the  13th  harmonic  gradually  into 
prommence  (see  Curves  XVIII.,  XIX.,  and  XV.).    It  is  very  difficult 


Curve  XVI.— No  Load  E.M.F. 
Wave.  93,700  yards  of  cable  con- 
nected. 


Curve  XVII.— No  Load  E.M.F. 
Wave.  93,700  yards  of  cable  con- 
nected. 


Curve  XVIII.— No  Load  E.M.F. 
Wave.  71,200  yards  of  cable  con- 
nected. 


Curve  XIX.— E.M.F.  wave.   51,800 
yards  of  cable  connected. 


to  obtain  good  results  under  these  circumstances,  for  if  resonance 
be  too  pronounced  the  oscillograph  motor  stops,  and  the  results 
cannot  be  noted.  I  do  not  think  that  Curve  XV.  shows  the  conditions 
of  maximum  resonance  by  any  means;  in  fact,  I  have  had  instan- 
taneous glimpses  of  alarming  resonance,  but  for  the  reasons  already 
stated  I  could  not  reproduce  them. 

I  used  to  think  it  a  safe  procedure  when  shutting  down  to  gradually 
slow  up  the  main  engine  and  let  the  voltage  die  down  gradually; 
similarly  it  was  my  opinion  that  one  should  excite  the  generator, 
and  run  up  slowly  on  the  cables  when  starting  up,  but  from  these 
experiments  it  is  clear  that  by  so  doing  one  passes  through  the 
conditions  for  maximum  resonance  with  all  odd  harmonics  above 
the  nth.  Undoubtedly  the  better  procedure  is  to  run  the  machine 
up  to  full  speed,  and  then  slowly  to  bring  up  the  excitation  to  the 
normal,  and  to  reverse  the  procedure  when  shutting  down. 


670 


FIELD:  A  STUDY  OF  THE   PHENOMENON   OF    [Glasgow, 


Curves  XX.  and  XXI.  more  nearly  approach  to  the  E.M.F.  curve 
of  the  alternator  on  open  circuit. 

Another  important  point  to  consider  is  whether  resonance  due 
to  a  higher  harmonic  can  occur  under  load  conditions.  The  curves 
generally  indicate  that  this  is  not  so,  the  ripples  being  apparently 
damped  down  to  a  minimum  under  load  conditions. 

Curve  XXII.,  which  was  taken  at  half  normal  load,  shows, 
however,  certain  ripples  accentuated,  and  the  question  is  worth 
inquiring  into. 

Look  at  Curve  XXIII.  We  have  already  seen  that  the  back 
E.M.F.  of  the  rotaries  being  a  smooth  curve,  the  higher  current 
harmonics  in  the  system  are  wattless,  and  are  either  capacity  or 
self-induction  currents.  The  current  ripples  which  flow  into  the 
rotaries,  representing  self-induction  currents,  no  doubt  partly 
neutralise  the  capacity  of  the  system,  but  at  the  high  frequencies 


srf 


Curve  XX.— No  Load  E.M.F.  Wave. 
9,150  yards  of  cable  connected. 


Curve  XXI.-  E.M.F.  Wave.  2,290 
yards  of  cable  connected 


Curve  XXII.— Taken  at  substation 
C  as  load  falls  off  between  11-12  p.m., 
125  amps,  at  power-station. 


Curve  XXIII.— E.M.F.  Wave 
Rotaries  on  no  load  (normal  excita- 
tion), 20-30  amps,  at  power-station. 


we  are  dealing  with  it  is  impossible  that  the  whole  capacity  effect 
can  be  thus  neutralised,  and  we  have  at  such  frequencies  as  275  and 
325  cycles  a  balance  of  capacity  effect  left  over ;  it  is  then  merely 
a  question  of  the  number  of  rotaries,  transformers,  and  cables  in 
service  which  decides  whether  or  not  partial  resonance  will  occur 
under  load  conditions. 

In  this  connection  it  must  be  borne  in  mind  that  if  r  is  the  ratio 
of  transformation  of  the  transformers  (in  the  case  in  question  r  =  20), 
a  coefficient  of  self-induction  in  the  low-tension  side  is  equivalent  to 
r^  (=  400)  times  the  coefficient  of  self-induction  in  the  high-tension 
side.  When,  again,  we  compare  the  capacity  and  self-induction 
currents  (for  the  same  voltage  applied)  at  a  high  frequency,  such 


1903.]  RESONANCE   IN   ELECTRIC  CIRCUITS.  671 

as  the  13th,  and  remember  that  the  former  varies  directly,  and  the 
latter  inversely  as  the  frequency;  we  see  that  even  a  large  wattless 
current  in  the  low-tension  side  J  due  to  self-induction  at  the  funda- 
mental frequency,  can  have  but  a  small  effect  in  neutralising  the 
capacity  effect  of  the  cables  at  the  high  frequency.  This  is  easily 
calculated  out. 

From  the  foregoing,  it  is  evident  that  it  should  be  easy  in  any 
particular  case  to  determine  experimentally  what  conditions  of 
capacity,  etc.,  will  give  maximum  resonance. 

For  example,  if  we  know  the  length  (/)  of  cable  which  produces 
resonance  with  the  p^  harmonic,  one  generator  only  working,  at  the 
speed  s  revolutions  per  minute,  we  know  that  the  length  which  will  give 

resonance,  with  the  ^'*  harmonic  at  a  speed  s,  will  be  /  (^  )  ;    again, 

if  two  generators  be  thrown  in  parallel,  we  halve  thereby  the  inductance 
of  the  circuit,  and  therefore  resonance  with  the  same  harmonic  will 
only  occur  with  twice  the  amount  of  cable  connected  to  the  circuit. 

This  fact  alone  will  usually  prevent  important  resonance  effects 
under  full-load  conditions,  the  period  of  greatest  importance  from 
this  point  of  view  being  that  of  light  load,  where  the  cable  system 
is  being  fed  from  one  generator  which  is  perhaps  of  relatively  small 
proportions. 

It  must  not  be  supposed  that  I  attach  great  practical  importance 
to  the  above  considerations  of  the  possibility  of  the  occurrence  of 
resonance;  as  a  matter  of  fact,  although  in  Glasgow,  I  was  for  a 
long  time  unaware  that  anything  of  the  kind  could  be  going  on,  we 
experienced  no  difficulty  at  all,  and  it  is  the  general  opinion  of  a 
great  many  experienced  engineers  with  whom  I  have  spoken  on 
the  subject  that  resonance  is  not  to  be  generally  feared  in  ordinary 
well-laid-out  systems. 

I  do  J  however,  consider  it  important  for  each  engineer,  as  far  as 
possible,  to  be  conversant  with  the  conditions  under  which  resonance 
is  Ukely  to  occur  in  the  system  under  his  charge,  and  to  avoid  the 
combination  if  it  is  at  all  likely  to  be  serious. 

It  is  further  conceivable  that  slight  resonance  effects  might  occur 
in  cable  circuits  supplied  by  continuous-current  machines.  All  such 
dynamos  have  a  ripple  of  a  high  order  present  in  their  E.M.F.  In 
the  case  of  a  rotary  converter  this  ripple  may,  as  we  have  seen, 
be  pronounced,  and  I  think  it  possible  that  considerable  resonance 
effects  might  be  found  in  such  cases*  It  would  be  interesting  to 
look  for  them. 


PART  II. 

The  second  part  of  this  paper  is  descriptive  of  some  experiments 
I  carried  out  to  examine  optically  the  ^ore  temporary  or  non-periodic 
effects  in  electric  circuits,  by  which  I  mean  such  effects  as  the 
growth  of  the  current  in  a  continuous- current  circuit  containing 
self-induction,  or  the  oscillatory  nature  of  the  charge  current  of  a 


672 


FIELD:  A  STUDY  OF  THE  PHENOMENON  OF     [Glasgow, 


cable  when  switching  it  on  to  a  direct-  or  alternating-current  circuit, 
and  other  similar  effects.  I  am  perfectly  aware  that  these  phenomena 
are  treated  mathematically  in  the  various  text-books  on  the  subject, 
but  I  still  think  the  experiments  highly  instructive. 

In  order  to  render  these  results  visible  on  the  desk  of  the 
oscillograph,  it  was  necessary  to  make  them  occur  periodically  and 
synchronously  with  the  motor  of  the  oscillograph.  I  therefore  con- 
structed a  contact  maker,  and  attached  it  to  the  shaft  of  a  disused 
tramway "  motor,  which  had  already  been  provided  with  two  slip 
rings  for  other  purposes.  The  motor  was  suppli^  with  direct 
current,  the  oscillograph  motor  connected  to  the  slip-rings,  and  the 
strips  suitably  connected  to  the  contact  maker.  The  latter  consisted 
of  a  continuous  ring,  and  a  second  one  cut  into  sixteen  equal  parts 


FiG.  i6a. 


v\AAAAAAA^||4 


^ 


Fig.  i66. 


with  provision  for  connecting  them  up  in  any  way  desired.  The 
motor  having  four  poles,  I  connected  the  contacts  in  four  groups  of 
four,  and  used  this  arrangement  throughout. 

Figure  i6  (a)  and  {b)  shows  my  general  arrangement. 

In  position  (a)  it  will  be  seen  that  the  charge  current  for  the 
combination  of  capacity  and  self-induction  passes  through  the 
oscillograph  strip  S ;  in  portion  (6)  the  combination  discharges 
through  S ;  this  process,  occurring  synchronously  with  the  vibrations 
of  the  oscillograph  mirror,  appears  as  a  stationary  curve  and  can  be 
photographed  as  heretofore.  The  photographs,  which  I  here  re- 
produce, had  an  average  of  30  seconds  exposure. 

Curve  XXIV.  represents  an  ordinary  make  and  short-circuit  without 
self-induction  or  capacity. 


1903.] 


RESONANCE   IN  ELECTRIC   CIRCUITS. 


673 


Curve  XXV.  represents '  the  growth  of  the  current  in  a  circuit 
containing  a  transformer  on  open  circuit. 

Curve  XXVI.  represents  the  above,  but  with  half  of  the  high-tension 
^rinding  short-circuited  through  a  single  lamp. 

Curve  XXVII.  represents  the  same,  but  with  the  whole  high-tension 
vrinding  short-circuited  through  the  incandescent  lamp. 

The  annihilation  of  the  self-induction  due  to  the  short-circuited 
secondary  is  noteworthy.  I  have  used  the  curves  thus  photographed 
for  the  determination  of  the  coefficient  of  self-induction  of  a  circuit ; 


Curve  XXIV.— R  =  2425  ohms, 
L  =  O.  K  =  0,'.R.P.M.  =  750,  V  =  2-6 
volts. 


Curve XXV. — R  =  244  ohms,  L  = 
transformer  H.T.  open,  K  =  O,  R.P.M 
=  760,  V  =  3-9  volts. 


LT 


Curve  XXVI.— Same  as  XXV.,  but  Curve  XXVII.— Same  as  XXV., 
with  half  H.T.  winding  short-cir-  but  with  whole  of  H.T.  winding 
cuited.  ^  short-circuited. 

it  will  be  noticed  it  gives  the  value  of  the  coefi&cient  of  self-induction 
for  practically  zero  current,  since  the  current  through  the  oscillograph 
should  at  no  time  exceed  o'l  ampere.  As  such,  the  method  may 
prove  useful  to  others  who  have  an  osdilograph  at  their  disposal,  and 
I  will  therefore  illustrate  it  briefly. 


Fig.  17. 


We  know  that  the  law  of  curve  from  A  to  B,  Fig.  17,  is 

y  and  x  representing  distances  only,  and  being  measured  to  the  same 
scale. 

We  have  then  that  — -j-,  -  =  —  ^  ;  in  other  words,  if  we  measure 
y  for  each  value  of  x  from  the  curve,  and  plot  log^  y  and  x  to  the  same 
scale,  we  should  obtain  a  straight  line  not  passing  through  the  origin, 
and  with  a  negative  slope  equal  to  p. 


674        FIELD  :  A  STUDY  OF  THE   PHENOMENON  OF    [Glasgow, 


i' 


But  we  know  that  px^=j  /,*  ;  /,  being  the  time  occupied  by  the 


discharge  from  A  to  B.    .  • .  L  in  secohms  = 


pxXz 


R  being  in  ohms,  and  ti  in  seconds. 

/,  is  of  course  easily  determined  by  the  speed  of  revolution  of  the 
contact  maker.  In  my  experiments,  /,  was  ^th  second.  It  is  to  be 
noticed  that  the  constant  of  the  oscillograph  or  deflection  per  ampere 
does  not  enter  in. 

It  may  be  urged  that  where  y  is  very  small  it  will  not  be  possible 
to  measure  it  accurately.  This  is  true  ;  the  curve  of  discharge  is  really 
asymptotic  to  the  zero  line,  log  0  equals  —  oo ,  hence  if  we  take  the 
zero  line  the  smallest  amount  too  high  or  too  low  we  should  get,  on 


Fig.  i8. 


Curve  XXVIII.— Shaded  Area 
defines  V  during  charge  and 
discharge. 


plotting  logarithms,  curves  either  running  out  to  infinity  within  a 
finite  time  or  becoming  parallel  to  the  zero  line  (see  Fig.  i8). 

We  can  get  over  this  difficulty  in  the  following  way.  We  know 
y  measured  from  the  true  zero  is  k^-^.  Let  us  write  y©  measuring 
from  false  zero  as  M  -f  A  f-^,  then 

dx       ~M  +  /fec-^*  ""  ""  ^^0 

that  is  measuring  the  slope  of  the  logarithmic  curve  reckoned  from  the 
.  false  zero  line  gives  us  an  inaccurate  result  in  the  ratio  of  y  to  y©  at  the 
point  in  question.  It  is  clear  then  that  the  logarithmic  curve  will  become 
more  and  more  nearly  straight  as  it  approaches  the  vertical  axis  of  y,  if 
therefore  it  be  produced  and  the  slope  measured  at  .this  point  we  know 

the  error  should  not  be  more  than  ^  at  the  origin,  which  in  my  opinion 

might  easily  be  kept  down  to  within  i  per  cent. 

If  before  drawing  the  logarithmic  curve  we  multiply  our  log  y 

values  by  -A ,  then  the  slope  will  be  such  that  if  we  mark  off  on  the 

vertical  axis  rs  to  represent  R  in  ohms,  s  /  will  represent  L  in  secohms. 


•  R 


Yj  /  is  a  mere  numeric  ;  the  dimensions  come  out  M®  L**  T°. 


1903.] 


RESONANCE  IN   ELECTRIC  CIRCUITS. 


675 


Curves  XXVIII.  and  XXIX.  represent  the  way  the  potential  rises 
at  the  terminals  of  a  self-induction  shunted  with  a  resistance  greater 
than  its  own  when  the  circuit  is  ruptured ;    the  connections  were 
made  as  in  Fig.  19,  the  curves 
explain  themselves.  1 

The  strip  Sa  being  connected         ^.—.^^^^^-VVVVVVVH 
across  the  self-induction  as  shunt         ^  ^  ^^^ 
really   acts    as    a     voltmeter. 
AVhen  the  discharge  takes  place 
the  same  current  flows  through 
each  strip,   the  rise  of  voltage 

is     therefore    represented    by  ;. 

0  6— Oa;  Oa  representing  the  Fig.  19. 

voltage   at    the   instant  before 

discharge.  Of  course,  by  making  r  large  enough  the  potential  across 
the  self-induction  might  be  brought  up  to  any  value  provided 
the  circuit  be  ruptured  with  absolute  suddenness,  i.e.,  no  spark 
occur  at  break,  and  there  be  no  eddy  currents  induced  anywhere  by 
the  circuit.  These  conditions  are,  of  course,  impossible,  but  it  is 
well  known  that  there  is  really  no  absolute  limit  to  the  rise  of  potential 
on  rupturing  a  circuit  possessing  self-induction. 

We  now  come  to  the  oscillatory  charge  and  discharge  currents 
in  circuits  containing  self-inductions  and  capacities.  These  experi- 
ments were  made  as  indicated  in  Fig.  16.  and  are  represented  in 
Curves  XXX.-XXXVI. 


Curve  XXIX.— Taken  from  Curve 
XXV^III.  ob-oa  represents  rise  in 
voltage  on  opening  circuit. 


Curve  XXX. 


Jf/\^s^^ 


■V--^ 


Curve  XXXI. 


Curve  XXXII. 


In  the  first  series  we  start  with  capacity  only ;  the  charge  and 
discharge  are  so  rapid  that  the  oscillograph  apparently  overshoots  the 
zero  line. 

The  exponential  term  in  this  case  is  c"*^  In  my  experiments  the 
capacity  was  1*5  x  lo^  farads,  and  resistance  roughly  25  ohms.  The 
maximum  self-induction  coefficient  was  approximately  '33  secohm  (it 
was  a  variable  self-induction  dep>ending  on  tl^e  current  strength),  the 


676        FIELD  :  A  STUDY  OF  THE   PHENOMENON  OF     [Glasgow, 

combination  thereforefhad  a  natural  frequency  of  about  225  cycles  per 

second. 

I  R  • 

We  see  then  that  ^^  =  2*67  x  10*,  and  y-  =  75,  that  is  the  process 

depicted  in  Curve  XXV.  as  happening  in  3'5th  second,  occurs  in  Curve 
XXX.  in  TTTTnrth  second.  Under  these  circumstances  the  natural  fre- 
quency of  the  oscillograph  strips  will,  of  course,  come  into  play. 

Curves  XXXI.-XXXIV.  represent  the  oscillations  in  the  self-same 
circuit,  as  the  self-induction  is  gradually  increased.  It  is  to  be 
noticed  throughout  that  the  resistance  in  circuit  on  discharge  is 
always  less  than  that  on  "make.**  An  examination  of  Fig.  16  will 
show  that  this  is  the  case. 

Curve  XXXIII  Curve  XXXIV. 

Curve  XXXV.  Curve  XXXVI 

Curves  XXXV.-XXXVI.  were  taken  with  exactly  the  same  apparatus^ 
with  the  exception  of  the  self-induction.  Here  a  different  transformer 
was  used.  I  reproduce  them  on  account  of  the  irregularities  at 
"make"  and  discharge.  I  cannot  quite  account  for  this.  I  certainly 
had  some  leakage  effects  going  on  in  the  circuit,  but  they  did  not 
seem  able  to  account  for  this  initial  irregularity.  There  was  another 
abnormality  which  I  noticed  on  closing  the  circuit ;  there  was  an 
instantaneous  oscillatory  curve  depicted  very  much  larger  than  the 
permanent  ones.  It  was  merely  instantaneous.  This,  again,  may 
have  been  a  charge  leaking  into  the  condenser  in  some  way,  but 
I  had  no  time  to  investigate  it  fully.  Perhaps  the  mathematicians  will 
tell  me  if  some  other  effect  is  possible,  and,  if  so,  it  would  be  well 
worth  while  to  try  and  repeat  it,  and  investigate  the  matter  further. 

Curves  XXXI.-XXXVI.  show  distinctly  how  rises  of  potential  occur 
on  switching  cables  cither  on  to  direct- or  alternating-current  machines. 

The  curves  themselves  are  curves  of  current,  but  we  know  that 
the  curve  of  E.M.F.  across  the  condenser  is  of  the  same  shape  but 
displaced  in  phase,  the  maximum  of  E.M.F.  occurring  when  the 
current  is  zero. 

In  this  case  it  is  easy  to  see  that  the  maximum  voltage  across  the 
condenser  will  reach  nearly  twice  the  steady  value,  thus  : — 

'At  the  moment  of  closing  the  switch  the  current  is  zero,  therefor^ 
the  ohmic  drop  is  zero. 


1903] 


RESONANCE   IN   ELECTRIC  CIRCUITS. 


677 


The  charge  in  the  condenser  being  zero,  v  is  likewise  zero  (see 
Fig.  20).  The  supply  EIM.F.  V  must  therefore  be  counterbalanced  by 
a  back  E.M.F.  in  the  self-induction  due  to  the  growth  of  the  magnetic 
flux. 

Now  the  voltage  across  the  self-induction  is  (V  —  r),  but  since 

C  =  K  -— ,  and  at  zero  time  C  =  O,  we  have  at  the  moment  of  closing 
the   switch  the  voltage  across  the  self-induction  or  V  —  r  =  V  and 


di 


o ;  this  means  that  this  voltage  starts  at  its  maximum 

value,  viz.,  V.    If  we  subtract  V  and  reverse,  we  get  the  voltage  across 
the  condenser  or  v.    The  oscillations  of  v  and  c  are  shown  in  Fig.  21. 

We  see  then  at  an  instant  after  the  start  or  at  the  end  of  the  time  of 
one-half  oscillation  the  voltage  v  has  risen  up  to  nearly  twice  V.  The 
voltage  across  the  cable  therefore  oscillates  about  the  constant  value  V, 
and  finally  settles  down  to  that  steady  value.  As  there  are  a  number 
of  important  particular  cases  where  such  oscillations  arise  in  general 
practice,  I  will  here  state  a  few  using  a  minimum  of  mathematical 
symbols. 


■0001)0000000"00"0"> 


:/f 


Fig.  20. 


The  differential  equation  which  holds  for  case  in  Fig.  20  is  of  the 
familiar  form — 


d'v 
dt^' 


R  dv  .V 

"^  TTdt    "^   LK 


LK 


(15) 


Now,  in  the  cases  we  are  about  to  consider,  V  may  have  a  constant 
value,  and  the  equation  applies  to  the  charge  portion  of  curves  XXXI.~ 
XXXIV. ;  V  may  be  zero,  as  in  the  case  of  the  discharge  portions  of 
the  same  curves ;  or  V  may  be  a  sine  function  of  the  time,  or 

Vo  sin  2  IT  «  /. 
In  the  first  case  we  know  the  general  expression 


v=zV  -h  A€ 


satisfies  equation  (15). 

I  =    R' 

If,  however,  t-jt  is  <:  -y^  the  discharge  is  no  longer  oscillatory 

and  we  shall  not  consider  these  cases. 

A  and  f  are  constants  depending  on  the  particular  conditions  of  the 
problem  which  must  be  fulfilled. 

If  V  is  zero,  the  solution  (16)  may  still  be  applied. 


678        FIELD:  A   STUDY   OF  THE   PHENOMENON   OF     [Glasgow, 

If  V  ^  Vo  sin  2  IT  «  /,  we  know  that  the  final  state  at  which  the 
voltage  V  will  arrive  will  likewise  be  a  sine  function.  We  can  write 
down  this  final  state  as 

Vosm2irnt  ,     s 

Where  0*  represents  the  operator  -ri ;  we  will  express  this  function 

as  V  =  vq  sin  (2  it  «/  4-  0*)« 

A  general  solution  which  will  be  applicable  to  the  initial  as  well  as 
the  final  state  of  things  will  therefore  be — 

V  =  Vb  sin  (2  irn  /  +  0^  +  Ac""  '  sin    |  \/{i^^^  -  \^  '  +  0)  (18) 

d  V 
The  current,  or  K  -v^  will  in  this  case  be  represented  by  the  expres- 
sion— 


C  =  2  IT  «  Kt-o  cos  (2  IT  fi/  +  0*)  +  — /^—  « 


2L 


Vlk 

'^"^  {  A^-^)  '  +  .  +  tan  -  V^-^^  }   (>8«) 

The  first  expression  representing  the  final  state,  and  the  latter  the 
initial  disturbance. 

We  shall  have  occasion  to  make  use  of  this  result  later. 

We  will  now,  however,  make  a  small  digression,  and  briefly  examine 
the  nature  of  the  oscillation  represented  by — 

V  =  A'c""    sin  jS  /  (  where  a  =      ?- 
1  2  L 


I  and 


We  will  take  the  case  where  the  voltage  across  the  condenser 
follows  this  law. 

The  coefficient  A  will,  in  lieu  of  a  better  term,  be  called  the  co- 
efficient of  the  oscillation,     v  will  be  zero  when  fi  tz=z  nw,  or  when 


'  =  -g^  ;  "  being  any  integer.    The  successive  zero  values,  therefore 

occur  after  equal  intervals  of  time,  viz.,  ^. 

The  maxima  will  occur  when  -—  =s  0; 

(it 

Hence  the  maxima  occur  when 


/3 
*  See  P6rry's  "  Calculus  for  Engineers." 


1903.]  RESONANCE   IN   ELECTRIC  CIRCUITS.  679 

This  shows  that  the  successive  maxima  occur  after  equal  intervals 

of  time,  viz.,  ^,  but  they  do  not  necessarily  occur  exactly  in  the  middle 

of  the  time-interval  between  the  two  successive  zero  values.    Since  the 

current  through  the  condenser  =  K  ^  ,  it  is  clear  that  the  zero  values 

of  the  current  occur  simultaneously  with  the  maximum  values  of  the 
voltage  across  the  condenser. 

if  V 

The  maximum  values  of  the  current  occur  when  ^^  =z  o,  or  when 

JL^  e"°'  (sin  /3/  -  2  tan-'  ^)^o 
L  K  \  a/ 

n  n 
i.e,y  when  /  = 


n  v  4-  2  tan-"*  ^^ 


The  current  maxima  therefore  do  not  necessarily  occur  simul- 
taneously with  the  zero  values  of  v. 

R«  1 

If,  however,  -j^  niay  be  neglected  in  comparison  with  -t— j-, 

tan-   -  =  :: 
a         2 

and  we  can  represent  the  current  by  the  expression — 

AK    -«/ 


Vlk* 


cos  j3  /, 


in  which  case  the  maxima  occur  half-way  between  the  zero  values, 

and  the  current  maxima  occur  simultaneously  with  the  zero  values 

of  V, 

_^/ 
Further,  in  this  case  and  with  the  oscillation  At    ^^  sin  ^t  the 

absolute  maximum  occurs  after  time  — ^,  the  value  being — 

AT   ^  T— » 
C     4  L 

and  in  the  case  of  the  oscillation  A  c" '  *-  cos  )3  /,  the  absolute  maximum 
will  be  equal  to  the  coefficient  of  the  oscillation,  viz.,  A,  i.^.,  the  oscilla- 
tion starts  at  its  absolute  maximum.* 

•  The  oscillation  represented  by  v  =  A«~  "  '  cos  f /3  ^  -  tan     ^  J  has  zero 

slope    f  or  -rj  —  0]  when  /  =  o.     This  is  the  true  form  of  the  oscillation 

/3  R' 

which  starts  at  a  maximum  value,  viz.,  A   -,--—..  -.    Where,  however,  -— - 

Ja^  -\-  (^  4  L' 

may  be  neglected  tan-*  —  =  o,  and  the  maximum  or  initial  value  is  A. 
Vol.  82.  45 


680        FIELD:    A   STUDY   OF    THE  PHENOMENON   OF     [Glasgow, 

In  the  cases  we  shall  consider  here  -  r^  is  negligible  with  regard  to 

I  ^ 

— 1^,  so  that  we  may  apply  the  above  simplifications,  and  write  as  the 

frequency  of  oscillation — 


J       /J 

2  7r^   Lk 


There  are  two  rules  which  it  is  of  importance  to  keep  in  mind  on 
account  of  their  bearing  on  the  voltage  and  current  rises  in  alternating- 
current  circuits  when  oscillations  arc  started.    They  are  as  follows  : — 

(i)  If  in  a  circuit  consisting  of  a  capacity  and  a  self-induction  a 
voltage  oscillation  be  started  of  which  the  initial  maximum  value  is  «^ 
the  coefficient  of  the  current  oscillation  will  be — 


CoV^ 


Lie 


2irn 

where  Co  is  the  maximum  value  of  the  condenser  current  after  the 
steady  state  has  been  reached  if  the  voltage  Vq  sin  2  tt  nt  is  applied  at 
its  terminals. 

(2)  If  a  current  oscillation  be  started  of  which  the  initial  maximum 
value  is  Co,  the  coefficient  of  the  corresponding  voltage  oscillation  will 
be— 


^v/lTc 


where  vo  is  the  maximum  value  of  the  voltage  wave  which  must  be 
applied  to  the  terminals  of  the  self-induction  in  order  that  the  current, 
after  the  steady  state  has  been  reached,  may  be  of  the  shape  Co  sin 
2irnL 

2Trn 

represents,  of  course,  the  ratio  of  the  frequency  of  the  oscillation  to  the 
frequency  of  the  supply  circuit.  These  rules  are  the  obvious  outcome 
of  what  has  preceded. 

We  will  now  return  to  the  treatment  of  the  case  where,  say,  a  cable 
is  switched  on  to  a  D.C.  generator  which  possesses  self-induction,  v  is 
represented  by  equation  (16). 

At  time  /  =  0  we  have  to  satisfy  the  conditions  rz=o  and-  -  =  o 

or  C  =  o. 

The  first  of  these  conditions  results  in  the  equation  V  =  —  A  sin  ^, 
and  the  second  shows  us  that  at  time  o  the  oscillation  starts  at  maxi> 
mum  or  crest. 

The  frequency  of  oscillition  will  be — 


1903.]  RESONANCE   IN  ELECTRIC   CIRCUITS.  681 

the  time  occupied  by  a  half  oscillation  will  be — 


^  LK""4L» 


.  at  time  /  = 


^  L  K  ""  4  L" 


i'  =  V  +  A«  "■'"     "■-•  sin  («  +  ,r) 

IT 

=  v(i4-e     ^/lik-l)      . (19) 

and  this  will  be  the  maximum  value  to  which  the  E.M.F.  across  the 
cable  can  rise. 

At  the  limit  ^^-j^  =  i,  which  is  the  limit  at  which  the  current  ceases 

to  be  oscillatory,  v^V  and  there  is  no  rise  of  voltage. 

We  cannot  take  a  negative  value  for  the  >/  terra  in  equation  (19), 
for  taking  the  negative  value  of  the  square  root  gives  a  result  for  some- 
thing that  was  happening  before  we  began  to  count  time.  It  has 
no  meaning  except  in  the  case  of  an  oscillation  having  been  started, 
and  the  zero  of  time  being  taken  at  some  period  subsequently. 

We  can  therefore  dismiss  this  case.  The  value  of  the  exponential 
in  (19)  must  therefore  be  between  i  and  o.    We  have  discussed  the 

latter  condition.    The  former  is  attained  when  -^^  =s  00.   Therefore 

when  R  or  K  is  very  small,  or  when  L  is  very  large,  v  will  rise  to  a 
maximum  of  practically  twice  V. 

It  is  interesting  to  think  of  the  case  where  a  voltage  V  is  suddenly 
applied  to  one  end  of  a  coil  of  large  self-induction  and  low  resistance, 
the  other  end  being  free.  The  interruption  in  the  circuit  is  equivalent 
to  a  very  minute  capacity.  An  extremely  rapid  oscillation  will  then  be 
set  up  through  the  coil,  and  the  potential  at  the  free  end  will  oscillate 
about  a  mean  V  with  an  extremely  high  frequency,  the  oscillation 
continuing  for  an  appreciable  time.  ,We  are  now  getting  into  the 
range  of  the  wireless  telegraphist.  In  the  case  of  a  cable  being 
switched  on  to  an  alternator  we  may  apply  the  self- same  result  if 
the  circuit  be  closed  at  the  maximum  of  the  E.M.F.  wave,  and  this  be 
sufi&ciently  flat  or  the  oscillation  sufficiently  rapid  for  us  to  assume  that 
there  is  no  appreciable  diminution  of  the  E.M.F.  during  the  time  of 
one-half  oscillation.  In  this  case  we  may  say  the  maximum  voltage 
will  be  nearly  twice  V,  and  under  other  conditions  less. 

If  the  cable  be  already  charged  and  have  a  potential  difference  at  its 
terminals  of  —V,  and  be  switched  on  to  a  circuit  of  P.D.  -f  V,  the 
maximum  to  which  it  can  be  subjected  will  be  nearly  3  V. 

It  will  be  seen  at  once  in  the  case  of  a  steady  voltage  V,  and  it  can 
be  shown  to  be  equally  true  in  any  other  case,  that  provided  R  is  small 
in  comparison  with  2  tt  w  L  in  Fig.  20,  the  voltage  across  L  due  to  the 


682       FIELD  :   A   STUDY  OF  THE   PHENOMENON   OF      [Glasgow, 

oscillation  is  at  every  instant  equal  and  opposite  to  v,  hence  we  have  the 
same  condition  as  that  for  resonance  during  the  steady  state,  viz.,  that 
a  current  flowing  through  a  self-induction  in  series  with  a  capacity 
produced  a  P.D.  across  the  former  equal  to  that  across  the  latter, 
but  opposed  in  direction.  In  these  initial  stages  we  are  therefore  also 
dealing  with  resonance  efiFects,  the  difference  between  that,  where 
we  have  a  steady  state  of  resonance,  we  have  to  adjust  L  and  K  so  that 

—  •     i  Y~i>  corresponds    to    the  frequency   of    the    supply    circuit. 

During  the  unsteady  state  we  have  resonance  with  any  values  of  L  and 
K,  for  given  an  initial  pulse  of  E.M.F.  or  current,  the  frequency  of 

oscillation  (w,)  will  be  self-adjusting  so  that  still  2irn,  ^     TTl?*     ^^ 

^  L*  l\. 

the  circuit  in  Fig.  20  be  closed  when  the  E.M.F.  is  zero,  the  steady  state 
is  not  instantly  reached,  for  this  would  imply  that  the  current  into  the 
cable  was  very  nearly  at  its  maximum  value,  but  we  know  that  it  will 
be  zero.  We  have  therefore  to  consider  the  expotential  term  in  equa- 
tion  (18). 

The  conditions  we  have  to  satisfy  arc,  at  time 

/  =  0        V  =  0 

T^  =  0        and  ^  =  0 
a  I 

C  =  0 

The  first  condition  is  already  satisfied  where  V  =  V©  sin  2  r  » /. 

The  second  involves  vo  sin  0*  -f-  A  sin  ^  =  0 (20) 

The  third  involves — 

A  K  (  /  \  ) 

2  9r  «  K  z^o  cos  0»  -f    -JyIc  ^°s  ]  ^  +  ^^""^  (~)  [  ~  ^     •  ^^^) 


These  conditions  merely  state  that  the  initial  value  of  the  voltage  and 
current  oscillation  are  equal  and  opposite  to  the  values  of  voltage  and 
current  which  exist  after  the  steady  state  has  been  reached  at  the 
moment  of  the  E.M.F.  wave  when  V  passes  through  the  zero. 

We  can  of  course  solve  equations  (20)  and  (21),  and  obtain  A  and  f 
in  terms  of  vo  and  0'  which  again  are  determinable  from  equation  (17). 

But  in  the  case  under  consideration  we  can  cut  this  short  in  the 
following  manner  : — We  know  that  the  P.D.  across  the  self-induction 
(which  is  the  self-induction  of  the  generator)  is  practically  directly 
in  line  with  V,  in  other  words  0'  =  0,  and  therefore  also  0  =  0.  There 
is  still  another  condition  which  must  be  true  at  time  /  =  0.  We  know 
that  at  every  instant  the  P.D.  across  the  self-induction  =  V  —  v,  but 
(V  —  2^)  may  be  expressed  as  : — 

at  time  /  =  0  this  is  also  zero,  and  therefore  if  R  is  small  in  comparison 

dt' 


with  L  (which  is  the  case  with  every  alternator)  we  may  say  -t-7  ^  0  at 

zero  time. 

This  last  condition  shows  us  that  at  the  mpii[ient  of  starting,  the 


190S.] 


RESONANCE   IN   ELECTRIC  CIRCUITS. 


688 


current  oscillation  has  its  maximum  value,  which  is  equal  and  opposite 
io2irnKvo.  We  may  therefore  say  at  once  that  the  coefficient  of  the 
oscillatory  voltage  is — 

2  IT  ti 


vo 


y 


I 

LK 


This  will  be  a  very  small  oscillation  which  starts  when  vo  is  zero  ; 
the  rise  of  voltage  across  the  cable  will  therefore  be  very  small  if 
switched  in  at  the  moment  of  zero  E.M.F.,  but  there  will  be  a  current 
oscillation  of  which  the  initial  value  equals  the  maximum  value 
after  the  steady  state  has  been  reached. 

I  do  not  propose  to  lengthen  out  this  inquiry  by  going  into  other 
more  complicated  cases,  such  as  switching  on  cables  with  transformers 
connected  across  the  ends,  or  switching  on  circuits  to  generators 
already  loaded  on  other  circuits,  since  in  no  case  are  greater  rises 


Fig.  21. 


of  potential  called  into  existence  by  initial  disturbances  than  those  we 
have  already  considered. 

I  will  therefore  take  up  the  special  case  of  switching  off  a  cable 
circuit  already  loaded  with  a  highly  inductive  circuit,  such  as  lightly 
loaded  transformers,  or  worse  still,  a  circuit  opening  on  the  high- 
tension  side,  the  low-tension  circuit  being  loaded  on  an  inductive 
load. 

Two  limiting  cases  are  those  of  special  interest — (i)  When  the 
circuit  is  broken  at  the  moment  the  current  is  passing  through  zero  ; 
(2)  when  the  circuit  is  broken  at  the  instant  the  current  is  at  its 
maximum. 

Dealing  first  with  the  case  of  a  bank  of  transformers,  the  secondary 
of  which  is  on  open  circuit. 

Let  the  maximum  of  the  charging  current  of  the  cable  be  Cg  and  of 
the  transformers  C^,  then  we  have  the  relations — 

Cjj  =  4  TT*  w'  L  K  Cl  and  2  tt  n  L  C^  =  Vo 

If  the  circuit  be  opened  at  the  moment  the  current  Cj^  and  C^  are 


684        FIELD:  A  STUDY  OF  THE  PHENOMENON  OF     [Glasgow, 


zero,  the  voltage  being  vo  or  the  maximum  of  the  steady  state,  it  is  clear 
that  there  will  be  excited  a  voltage  oscillation  starting  with  a  maximum 

value  of  Vo.    The  coefficient  of  the  current  oscillation  will 


^^  Vt*^' 


that  is  to  say,  the  coefficient  is  to  C^  in  the  ratio  of  the  frequency  of 
oscillation  to  n  ;  and  to  Cl  in  the  inverse  ratio.  There  will,  however, 
be  no  rise  of  voltage. 

If  the  circuit  be  opened  when  Cl  and  Cg  are  at  their  maximum 
values,  or  when  the  voltage  is  zero,  a  current  oscillation  will  be  excited 
starting  with  the  maximum  value  C^. 

The  coefficient  of  the  voltage  oscillation  will  then  be  y/h  Cl,   that 

IV 

is  to  say,  the  coefficient  is  to  vo  in  the  ratio  of  the  frequency  of 
oscillation  to  the  frequency  «.  This  will,  of  course,  usually  result 
in  a  considerable  rise  of  potential.  If  the  secondary,  however,  be 
not  an  open  circuit,  it  may  act  more  or  less  as  a  short-circuited 
turn  and  either  damp  down  the  violence  of  the  oscillation  if  the 
secondary  circuit  be  non-inductive,  or  increase  the  violence  of  the 
same  if  the  load  be  very  inductive.     In  any  case  the  eflFect  of  the 


Fig.  22. 


secondary  may  be  represented  by  a  shunt  circuit  in  the  primary,  thus 
in  Fig.  22,  /j  represents  a  choke  coil  having  the  same  self-induction 
coefficient  (Z,)  as  the  primary  circuit  of  .the  transformer  on  no  load. 
R,  La  represent  the  resistance  or  self-induction,  as  the  case  may  be, 
which,  when  connected  in  parallel  with  /,  will  behave,  as  far  as  the 
supply  circuit  is  concerned,  as  does  the  transformer  on  load.  If 
the  transformer  supplied  motors,  it  would  be  necessary  to  include 
in  the  shunt  circuit  a  back  E.M.F.  Taking  the  worst  case,  where  the 
secondary  circuit  is  loaded  inductively  at  the  moment  of  interrupting  ; 
it  is  clear  that  during  the  oscillation  that  follows  the  total  energy 
of  the  system  will  be  at  one  instant  stored  electro-magnetically  in  the 
magnetic  field  interlinked  with  the  circuit,  at  another  electro-statically 
in  the  capacity. 

The  total  energy  at  the  moment  of  interrupting  is 

the  first  term  representing  the  total  energy  stored  in  the  capacity 
in  watt-seconds  at  the  moment  of  interrupting,  K  being  tne  capacity  and 
V  the  voltage  at  the  terminals  at  the  moment  in  question  ;  the  second 
term  being  the   watt-seconds  stored  in  the  transformer  due  to  its 


1903.] 


RESONANCE   IN  ELECTRIC  CIRCUITS. 


685 


magnetic  state,  C,  C,  being  the  primary  and  secondary  current  at  the 
moment  of  interrupting,  and  <r,  (r,  the  number  of  turns  of  primary  and 
secondary  respectively;  while  the  last  term  represents  the  energy 
stored  electro-magnetically  in  the  secondary  external  circuit ;  L  being 
coefficient  of  self-induction  of  this  external  circuit.  * 

The  maximum  value  of  the  voltage  oscillation  will  be  slightly  less 
than  V,  where 

This,  of  course,  is  readily  calculable;  it  will  represent  a  very  con- 
siderable and  usually  a  highly  destructive  rise  of  potential. 

As  a  last  example  of  the   kind,   we  will  consider  the  oscillation 
in   a  circuit  consisting  of  a  capacity    and  self-induction,  where  at 
the  moment  of  the  interruption 
the  voltage  across  the  capacity 
is  —  r„  and  the  current  flowing 
through  the  self-induction  is  C,. 

We  can  consider  the  voltage 
oscillation  as  the  resultant  of 
two  components,  the  first  given 
by  the  conditions  whep  /  =  o, 
p  =  o,  C  =  C„  the  second  given 
by  the  conditions  when  /  =  <?, 
r  =  —  r„  0  =  0.  It  is  clear 
that  the  sum  of  these  oscilla- 
tions will  satisfy  the  fundamental  equation,  and  the  initial  conditions, 
viz.,  when  /  =  o,  v  =  —  v„  C  =  C,. 

We  have,  however,  already  considered  both  components  separately, 
and  can  write  down  the  oscillations  forthwith  in  their  approximate 
forms,  as ; — 

.  =  -  ..  rr.'  COS  (yj^)  /  +  C.  yC  ,- A'  ,,,  (yii) , 

C  =  r.  ^l  rr.'  sin  (^^j  l  +  C.  r-V  cos  (^/J^)  , 
or — 

I  could  ha^e  obtained  these  results  by  means  of  the  oscillograph 
had  I  thought  my  capacities  would  have  stood  the  severe  strain. 
The  connections  would  have  been  as  in  Kig.  23.    The  current  curve 


Fig.  23. 


686      FIELD  :  A  STUDY   OF  THE   PHENOMENON   OF      [Glasgow, 


through  S  would  then  be  of  the  nature  shown  in  Fig.  24.    If  we  make 
the  resistance  in  the  battery  circuit  one-half   that  in  the  condenser 

circuit,  we  have  the  exponential 
terms  during  both  charge  and 
discharge  operations  the  same ; 
in  other  words,  the  curve 
representing  the  oscillation 
will  be  found  to  just  fit  into 
the  cone  formed  by  taking  two 
of  the  curves  ABC,  repre- 
senting the  charge  period. 
This  is  shown  dotted  in  the 
diagram. 

A  few  words  with  regard 
to  the  frequency  of  oscillation 
of  which  we  have  been  speak- 
ing. 

A  5, 000- volt  cable  of  such 
length  as  to  give  i  microfarad 
capacity  connected  to  a  trans- 
former of  which  the  .magnet- 
ising current  was  i  ampere 
at  50  CkJ,  or  with  an  L  of 
15*9  sccohms,  would  resonate 


2  IT    V     15*9 


with  a  frequency  .  , 

or  40  cycles  per  second.  A 
generator  on  the  other  hand 
which  would  give  a  short- 
circuit  current  of  200  amperes, 

or  with  an  L  of   ^5^    secohms 
200 

would  produce  an  oscillation  of 

frequency  of  40  x  ^200  =  560. 

In  large  systems  the  oscillations 

produced     on     switching    on 

cables  to  their  generator   will 

usually  be  of  a  much  higher 

order  than  those  produced  in 

the  system  on  switching  ofiF. 


PART   III. 


We  have  up  to  the  present  assumed  that,  provided  the  3-phase 
system  be  symmetrical,  the  capacity  effect  of  the  cables  may  be 
exactly  reproduced  by  substituting  in  place  of  the  cables  conductors 
without    capacity,   but     with    a    single    combination    of    capacities 


^ 


1903.]  RESONANCE   IN  ^ELECTRIC  CIRCUITS.  687 

connected  between  Ihem  and  earth,  as  represented  in  Fig.  14.  We 
know,  however,  that  this  is  not  strictly  true ;  a  3-core  cable  really 
can  only  be  represented  by  a  distributed  capacity,  as  in  Fig.  25, 
where  ABC  represent  the  3  cores,  and  the  dotted  line  an  imaginary 
earthed  conductor  of  zero  resistance.  Now,  if  in  this  case  an  E.M.F. 
be  suddenly  applied  at  one  end  of  the  cable,  the  other  being  open- 
circuited,  the  whole  cable  does  not  become  instantly  charged;  uc, 
the  current  at  the  point  px  in  core  A  will  have  a  difiEerent  value 
from  that  at  point  ^  at  every  instant.  Further,  the  potential  at  ^, 
above  earth  will  not  be  the  same  as  that  at  /►,»  and  the  quantity  of 
electricity  charging  the  cable  per  cm.  length  at  p^  will  be  different 
from  that  at  ^a. 

On  the  other  hand  a  definite  and  appreciable  time  will  be  necessar}' 
for  the  charge  to  be  felt 
aU  along  the  cable.  A      x  J,J- J-X-L  JLXX  J-J-O, 

We  have,  in  fact,  the  £. J.J.J.J. J. J.^.J. J^.j:.^ 

same  sort  of  problem  as      «       -r-r-rnr"rT"r~rTT"rT    | 
that   of  sending  signals  J* 

through      the      Atlantic  ^'^"X'X'X'X'XXUrXiru:" 

cable,  where,  if  a  pulse     ^ 
of  E.M.F.  or  current  be 
injected   into  the  cable 

at  one  end,  an  appreci-  ^^'  ^^ 

able  time  is  required 
before  the  pulse  is 
manifested  at  the  far 
end. 

What  goes    on    may 
be  briefly  sUted  to  be  as  ^^®-  2^- 

follows : — 

If  at  any  instant  the  potential  at  i  (Fig.  26)  is  zero,  and  current 
is  flowing  from  2  to  i,  the  potential  at  2  will  be  positive,  which  means 
that  the  capacity  K  must  have  a  definite  charge  while  that  of  *,  is 
zero. 

Again,  if  current  is  flowing  from  5  to  4  to  3  to  2,  the  potential  at  5  will 
be  higher  than  4,  of  4  than  3,  of  3  than  2  ;  hence  the  charge  in  ^5  is  greater 
than  that  in  ^4 ;  of  ^4  than  k^ ;  of  ^3  than  K-  Now  every  capacity  takes  an 
appreciable  time  to  charge,  and,  therefore,  there  will  be  a  time-growth 
of  charge  along  the  cable,  *,  arriving  at  its  full  charge  last. 

Now  let  us  assume  that  by  the  time  ^,  has  received  a  definite  charge 
the  potential  at  the  sending  end  has  been  gradually  reduced  to  zero ; 
the  charge  in  the  initial  capacity  will  then  be  zero,  and  in  the 
final  capacity  k^  a  maximum.  We  have  then  the  exact  reverse  of 
the  initial  state  when  the  charge  in  k^  was  a  maximum  and  in  k,  zero. 
There  will  now  be  a  return  current  tending  to  equilibriate  the 
potential  along  the  conductor.  This  return  or  reflected  wave  will 
require  a  definite  time  interval  to  reach  the  sending  end,  and  if  the 
applied  E.M.F.  at  the  sending  end  is  periodic,  and  the  returning 
waves  synchronise  with  the  applied  periodic  E.M.F.,  a  state  of 
resonance  will  be  set  up.    This  might  reach  dangerous  proportions, 


h           7           9            €           ^           3           9            1 

JL^     fr     Yi     V€     K     y^i     ^9     Wf. 

^^^AA^A^f^^A^f^ 

688        FIELD  :  A  STUDY   OF  THE   PHENOMENON  OF    [Glasgow, 

a  small  E.M.F.  at  the  sending  end  involving  an  extremely  high  P.D. 
at  the  far  end. 

I  have  worked  out  this  case  for  a  3-core  cable,  with  an  impressed 
E.M.F.  at  one  end,  consisting  of  a  fundamental  of  25  cycles  and  a 
13th  harmonic;  but  find  that  the  length  of  cable  required  before 
a  dangerous  state  of  resonance  is  set  up  is  far  beyond  anything 
at  present  in  use  in  this  country  for  power  transmission  purposes. 
I  do  not  propose  to  give  the  full  mathematical  details  of  this  problem 
as  they  may  be  found  elsewhere. 

As,  however,  this  particular  case  of  the  general  problem  is  inter- 
esting to  electrical  engineers,  I  propose  to  apply  here  the  solution 
of  the  same  to  a  practical  case. 

We  will  confine  our  attention  to  a  3-core  lead-sheathed  high- 
tension  cable  ;  area  per  core  =  '2  D" 

Let  p  =  resistance  of  i  core  per  mile  =  '22  ohm. 

Let  K  =  equivalent  capacity  per  leg  per  mile  (see  Fig.  i2^)  = 
•5  X  10-*  farads. 

Let  X*  =  coefficient  of  self-induction  per  core  per  mile  {i.e,,  X  is  a 

coefficient  such  that  volts  drop  in  each  core  per  mile  =  p  c  -h  X  ^.j. 

Let  c  be  the  current  at  any  point  and  at  any  time,  flowing  axially 
along  the  conductor  under  consideration. 

Let  V  be  the  potential  above  earth  at  a  similar  point. 


Fig.  27. 

We  need  only  consider  one  core,  and  may  think  of  it  as  consisting 
of  a  conductor  as  represented  in  Fig.  27. 

The  cable  is  on  open  circuit  at  the  far  end  ;  at  the  near  end  a  sine 
wave  of  E.M.F.  is  applied. 

The  fundamental  differential  equations  of  the  problem  are  : — 

_    =p._    +    X._ (22) 

__=p«._    +X._._ (23) 

^^  =  -«^v-; (24) 

dx  d  t 

♦  I  here  represent  resistance,  coefficient  of  self-induction,  and  capacity 
per  unit  length,  by  Greek  letters,  as  these  quantities  are  of  different  dimensions 

from  the  R  L  K  previously  employed  ;   we  saw  that  ^J  :^  was  of   the 
dimensions  of  a  frequency  or  /- ,    we  soon  shall  see  that  ^/  ^-  represents  a 

velocity  or  --^— .    It  is  of  importance,  in  order  to  avoid  a  confusion  of  ideas, 
to  keep  this  point  well  in  mind. 


1903.]  RESONANCE   IN  ELECTRIC  CIRCUITS.  689 

A  solution  for  v  is — 

»  =  Vo  €**  sin  (2  IT  »  /  +  a  x)f 
and  for  current — 

c  =  Co  €**  sin  (2  IT  w  /  H-  a  4?  +  i//). 

These  solutions  would  apply  to  the  case  of  a  cable  infinitely  long  ; 
we  have,  however,  to  satisfy  the  terminal  conditions — 

when  4:  =  <?,  V  =  Vo sin  2  irn  /, 
when  x  =  lfCsso, 

I  being  the  length  of  the  cable  in  miles. 

The  particular  solutions  which  satisfy  these  terminal  conditions 
are: — 

V  =  Vx  €~**  sin  (2  ir  n  /  —  a  x  +  <^)  + 

V,  e-M^-*)  sin  (2  IT  n  /  —  a  (2  /  —  jr)  +  ^) 

_  2xnicV,  1^"'*  sin  (2  IT  «  /  —  a  ;r  +  ^  +  e)  —  l 

^  ~   Va,"+  a,»(e-«(»/-*)  sin  (2  irn  /  —  a  (2  /  —  ^)  +  ^  +  «)) 
where    a  =  Vtt  n  k  (I  —  2  ir  »  X) 
a  =   J'/r  n  K  {I  -|-  2  Trn  X) 
1=  ^»  +  4  ^  «'  X» 
V —  ^^ 

^«  ^  -4a/  —2a/ 


/  —4a/  —2a/ 

i^  I   +  €  +  2  *  cos  2  a  I 


tane  =- 

a 

-J  a/ 

c         sin  2  o  / 
tan  ^  =  zri^, 

I  4-  €         cos  2  a  I 

An  examination  of  the  form  of  the  solution  of  v  and  c  shows  that 
each  consists  of  an  original  plus  a  reflected  wave.  If  the  cable  had 
a  length  of  2  /,  then  the  first  term  gives  the  value  of  the  original 
wave  at,  say,  the  point  />, ;  the  second  the  value  of  the  same  wave 
at  point  Pa  (Fig.  28),  and  the  solution  tells  us  that  in  the  case  of  the 
cable  of  length  /,  the  actual  value  of  the  wave  at  p^  is  in  the  case 
of  the  E.M.F.  the  sum  of  the  value  at  pi  and  />,  at  every  instant  ; 
in  the  case  of  the  current  the  actual  wave  at  />,  is  the  difference 
between  the  values  at  p^  and  /►a. 

It  will  be  noticed  that  the  differential  equations  (22),  (23),  (24), 
which  obtain  for  the  case  in  question  involve  three  conditions : — 

(ist)  If  we  consider  any  particular  short  portion  of  a  given  cable 
such  as  a  6,  the  quantity  of  electricity  entering  this  portion  axially 
at  a  in  a  given  time  is  equal  to  the  quantity  leaving  axially  at  6,  plus  the 
accumulation  of  electricity  at  the  side  walls  bounding  the  portion  a  b. 


690       FIELD:  A   STUDY   OF  THE   PHENOMENON   OF      [Glasgow, 

(2nd)  The  accumulation  of  electricity  as  above  is  equal  to  the 
pressure  obtaining  at  the  portion  of  the  cable  a  b,  multiplied  by  a 
constant  depending  on  the  nature  of  the  containing  walls,  and  not 
on  the  conductor.  If  this  constant  is  zero  there  can  be  no  accumula- 
tion, and  the  quantity  entering  a  equals  the  quantity  leaving  at  b. 
The  above,  which  merely  state  the  electrical  conditions,  are  obviously 
those  for  an  incompressible  fluid  flowing  through  a  pipe  with 
elastic  side-walls.  For  if  the  side-walls  be  rigid  there  can  be  no 
accumulation  in  any  portion  of  the  tube;  if  elastic,  the  quantity 
entering  any  cross-section  such  as  a  equals  that  leaving  another 
cross-section  6,  plus  the  accumulation  in  the  portion  a  6,  this 
accumulation  taking  place  in  virtue  of  the  elasticity  of  the  side-walls, 
and  not  being  due  to  any  compressibility  of  the  fluid  itself. 

The  3rd  condition  is  that  the  potential  gradient  at  any  moment 
and  at  any  cross-section  is  the  sum  of  two  factors — the  first  propor- 
tional to  the  quantity  per  second  passing  the  cross-section  at .  that 


2l'C0 

-ac — 

nr           -At    ff    ^1,    fM    ^^ 

— ^ 

**      Y  ^  *  y  •!* 

A.      J ,       Ax, 

^"■"" 

^"^ ' 

t 

t 

t^G.  28. 

moment,  and  second  proportional  to  the  quantity  per  second  per 
second  or  the  acceleration.* 

This  last  condition  would  similarly  hold  for  a  fluid  possessing 
inertia,  and  being  retarded  in  its  passage  by  true  fluid  friction  (f.^., 
loss  of  head  oc  velocity).  Now  all  these  three  conditions  will  very 
nearly  obtain  in  the  case  of  water  flowing  through  an  indiarubber 
tube.  This  is  a  most  useful  analogy  to  fix  our  ideas  of  what  goes 
on  in  a  cable.  (It  will  be  noticed  that  the  stnalogy  of  an  organ  pipe 
which  has  been  proposed  is  quite  inaccurate,  for  in  this  case  we 
should  be  dealing  with  a  compressible  fluid  in  a  pipe  with  rigid 
containing  walls.)  I  should  like  to  see  a  model  made  consisting  of  a 
suitable  elastic  tube  with  a  blind  end  in  which  was  included  a  small 
reciprocating  pump.  In  this  way  we  should  be  able  to  follow  the 
propagation  and  reflection  of  the  waves,  also  the  propagation  of 
individual  wave  fronts,  a  most  important  point  which  we  shall  touch 
on  later.  It  is  to  be  observed  that  the  hydrostatic  pressure  at  any 
portion  of  the  tube  corresponds  to  the  electric  potential  at  any 
portion  of  the  cable,  while  the  velocity  of  the  fluid  corresponds  to 
the  current  strength. 

We  shall  obtain  maximum  resonance  when  a  /  =  -  :  or  when  /  =r —  • 

2  2a 


The  equation  representing  this  in  the  electrical  case  will  be 


1903.]  RESONANCE   IN   ELECTRIC   CIRCUITS.  691 

In  this  case  the  E.M.F.  at  the  sending  end  will  be  of  effective  value  Vo ; 
and  at  the  receiving  end — 

-  -  tan  ^ 
2  6      ^  Y 

Vl    +€~" 


—  2c 


or     -HI'—-  . 

I   —  f—irUn0 


We  will  apply  these  conclusions  to  the  case  of  a  50  cycle  circuit, 
containing  a  13th  harmonic  or  where  n  =  650  CXJ  X  can  be  calculatejd 
from  the  formula — 


X=(log,  ^  +  i)  10-^x3-22 


where  b  =  distance  between  cores,  a  =  radius  of  each  core. 

Let  us  take  a  =  '275  a"  6  =  '8",  then  X  per  core  per  mile  =z  -000502 
secohm. 

If  we  say  roughly  that  at  this  frequency  2  irnX  ^  10 p 

.     ^  /I— 2  7r«X  i-^^^..^^ 

tan  6* 

and    ?-?-^ =  127. 

I    —  € 

It  follows  then  that  13th  harmonic  will  be  magnified  127  times  at 
the  end  of  the  cable. 

Putting  in  the  at)ove  values  of  p,  c,  and  X  in  the  expression  ~     we 

have  /  =s  23*5  miles. 

It  appears,  therefore,  it  is  quite  within  the  region  of  possibility 
for  this  class  of  resonance  to  occur  on  a  system  of  moderate  frequency, 
supplying  very  long  cables,  and  with  slotted  armatures  containing 
two  or  more  slots  per  pole  per  phase.    This  case,  though  of  importance 

•  This  formula  gives  half  the  value  of  the  self-induction  of  a  circuit  made 
up  of  two  parallel  wires.  In  the  3-phase  case  the  current  in  core  i  is  at 
every  instant  equal  to  the  sum  of  the  currents  in  2  and  3.  Now,  the  effects 
of  the  currents  in  2  and  3  on  i  will  be  independent  of  their  relative  positions, 
provided  their  radial  distance  from  i  is  not  changed — we  can  therefore 
consider  them  coincident,  and  calculate  the  effect  on  i  as  in  the  single-phase 
case.  We  may  consequently  take  the  self-induction  of  a  loop  with  the 
same  current  per  line  as  in  i,  halve  it  and  consider  this  the  E.M.F.  of 
self-induction  acting  in  each  of  the  line  wires  i,  2,  and  3  at  right  angles  to 
the  currents  in  those  line  wires.  It  is  interesting  to  note  that  this  formula 
will  give  the  same  result  per  line  wire  as  if  we  calculate  the  self-induction 
of  the  inner  of  a  concentric  cable,  the  inner  being  of  the  same  diameter 
as  each  core  in  the  3-phase  cable,  and  the  radius  of  the  outer  being  the 
same  as  the  distance  between  centres  of  the  three  individual  cores,  provided 
this  dimension  is  large  in  comparison  with  the  radial  thickness  of  the  outer 
conductor. 


692        FIELD  :  A   STUDY   OF  THE   PHENOMENON   OF    [Glasgow, 

in  electrical  engineering,  and  deserving  of  careful  consideration,  need 
not  necessarily  cause  uneasiness. 

The  value  of  the  P.D.  due  to  the  harmonic  at  any  intermediate 
point  of  the  cable  will  lie  between  V^,  and  127  V^. 

It  is  well  known  that  the  capacity  effect  of  these  long  cables  can 
be  imitated  almost  perfectly  by  connecting  up  a  number  of  smaller 
capacities  with  wire  containing  resistance  and  self-induction,  and  I 
suggest  it  would  be  a  subject  of  vast  interest  if  some  one  would 
investigate  this   matter   experimentally  rather  than  mathematically. 

It  is  to  be  noted  that  since  —  is  the  wave  length  of  the  space  wave 

a 

2  IT  tt 

in  the  cable,  the  velocity  of  propagation  is   ;  when  dealing  with 

such  high  frequencies  that  we  can  a£Eord  to  neglect  p,a  =  2irn  ^ \k, 
and  the  velocity  of  propagation  becomes  v -^  miles  per  second. 

If  X  =  5  X   io-<,  and  c  =  -5  X   10-*  ;  V    x~  "^  63,200  miles  per 

second,  or  approximately  J  the  velocity  of  light. 

There  is  still  an  important  aspect  of  the  subject  of  High  Potential 
Rises  in  circuits  containing  distributed  capacity,  self-induction,  and 
resistance  (and  every  circuit  does  to  a  greater  or  less  extent)  which 
I  have  not  touched  upon.  I  refer  to  the  initial  disturbances  in  such 
circuits  when  the  potential  at  any  one  point  is  suddenly  altered. 
The  subject  is  a  very  difficult  one  to  treat  mathematically  in  at  all 
a  general  manner ;  it  must  therefore  be  experimentally  investigated. 
I  doubt  even  if  the  oscillograph  will  be  of  much  aid  here  on  account 
of  the  extreme  rapidity  with  which  the  phenomena  take  place. 

A  most  interesting  paper  on  the  subject,  entitled  "  Static  Strains 
in  High-Tension  Circuits  and  the  Protection  of  Apparatus,"  was 
read  by  Mr.  Percy  H.  Thomas  before  the  American  Institute  of 
Electrical  Engineers,  14th  February,  1902,  which  is  well  worth  study 
by  all  who  are  interested  in  the  subject.  I  am  under  the  impression 
(I  hope  I  am  mistaken)  that  the  Proceedings  of  the  American  Institute 
of  Electrical  Engineers  are  not  read  on  this  side  with  the  attention 
they  deserve,  and  I  will  ask  pardon  for  briefly  explaining  here  the 
nature  of  the  so-called  "  Static  Strains"  of  which  the  above-referred-to 
paper  treats. 

In  Fig.  29,  S  represents  a  source  of  high  potential  (V).  A  B,  a 
circuit  or  line  of  any  nature  at  zero  potential. 

At  the  instant  before  closing  the  switch,  the  potential  is  represented 
by  the  full  black  line  in  Fig.  30.  Now  on  closing  the  switch  the 
line  A  B  cannot,  as  we  have  seen,  be  instantly  raised  to  the  potential 
V;  in  fact,  at  the  moment  of  closing,  the  potential  (assuming  no 
spark  occurs)  all  along  the  circuit  would  likewise  be  represented  by 
the  full  line  in  Fig.  30.  Instantly,  however,  the  charge  in  the  portion 
of  the  system  S  T  begins  to  distribute  itself  over  the  whole  system 
from  S  to  B,  the  first  effect  being  a  tendency  for  the  electro-static 
charges  in  the  neighbourhood  of  the  switch  to  equalise  themselves, 
resulting  in  a  moderation  of  the  steepness  of  the  potential  line,  as 
shown  dotted  in  Fig.  30. 


1903.]  RESONANCE   IN   ELECTRIC   CIRCUITS.  693 

This  potential  "  front "  will  then  travel  along  the  system  to  B,  be- 
coming modified  as  it  proceeds,  depending  on  the  constants  of  the  line 
and  circuit.  The  question  is,  what  is  the  potential  gradient  at  all  parts 
of  the  circuit  as  this  potential "  front "  reaches  them  ?  It  is  a  question 
of  vast  moment.  Every  one  who  has  worked  much  with  high-tension 
motors  and  transformers  will  have  experienced  difficulty  owing  to  the 
short-circuiting  of  turns  and  layers  in  a  most  curious  way.  I  have  seen 
the  winding  stripped  off  high-tension  motors,  the  insulation  of  which 


Fig.  29. 

was  punctured  with  innumerable  pinholes.  The  normal  voltage  be- 
tween turns  is  a  perfectly  definite  quantity,  and  accounts  in  no  way  for 
the  puncturing.  But  it  is  clear  that  if  a  potential  front  with  a  steep 
potential  gradient  traverses  the  winding,the  potential  difference  between 
neighbouring  windings  or  layers  may  be  very  excessive  in  comparison 
with  that  after  the  normal  steady  state  has  been  reached.  For  example, 
if  the  distance  a  in  Fig.  30  represents  the  length  of  two  layers,  it  would 
be  possible  to  have  momentarily  the  full  potential  of  the  circuit  across 
these  layers. 

On  switching  a  high-tension  motor  on  to  a  circuit,  both  poles  cannot 
be  closed  simultaneously.  On  closing  the  first  pole  we  have  the  state 
of  things  already  discussed  and  represented  in  Fig.  30.  The  potential 
front  on  reaching  the  dead  end  of  the  circuit  is  reflected  back,  there 


.1... 


\ 


v{ 


Fig.  30. 

occurs,  one  may  almost  say,  a  **  splash  "  of  potential,  possibly  analogous 
to  the  splash  caused  by  a  sea  wave  on  reaching  a  boundary  wall,  and 
similar  to  the  reflected  waves  we  have  already  discussed. 

The  same  thing  will  occur  on  closing  the  second  pole  of  the  circuit, 
only  in  this  case  the  height  of  the  potential  front  will  be  twice  what  it 
was  in  the  preceding  case. 

It  is,  of  course,  difficult  to  say  whether  the  strain  on  the  insulation 
is  greater  in  this  case  than  in  the  preceding ;  in  general,  we  may  say 
that  if  the  front  extends  over  a  distance  of  more  than  two  layers  of  the 
winding,  the  strain  will  be  determined  by  the  potential  gradient. 

These  potential  fronts  may  be  created  at  any  point  of  the  circuit  by 
suddenly  altering  the  potential  at  that  point,  eg.,  by  short-circuiting 
grounding,  and  the  like.- 


694        FIELD:  THE    PHENOMENON   OF   RESONANCE.      [Glasgow, 

This  is  a  subject  that  will  amply  repay  any  one  who  will  undertake 
a  careful  research. 

In  conclusion  I  should  like  to  state  how  very  powerful  a  weapon  in 
experimental  research  Mr.  Duddell's  oscillograph  should  prove.  There 
are  a  vast  number  of  investigations,  of  which  the  above  are  but  unhappy 
samples,  which  would  amply  repay  any  experimenter  to  carry  out.  It 
is  only  given  to  mathematicians  to  see  clearly  with  the  mind's  eye  the 
full  physical  interpretations  of  their  symbols ;  to  ordinary  engineers, 
such  as  myself,  who  make  no  pretensions  to  wielding  the  mathematical 
weapons,  an  optical  investigation  of  such  phenomena  brings  home  in  a 
clearer  way  than  pages  of  mathematics  what  is  really  going  on.  I 
would  suggest  that  the  study  of  the  effect  of  an  arc  on  opening  a  high- 
tension  circuit,  what  goes  on  in  sparks,  in  so-called  liquid  capacities 
such  as  are  used  for  starting  single-phase  motors,  determining  the 
hysteresis  loops  of  transformer  circuits  from  the  load  current  and 
voltage  curves,  and  a  number  of  other  equally  interesting  and  instructive 
series  of  experiments  which  suggest  themselves  at  once,  would  form 
the  ground-work  for  most  delightful  papers. 

These  subjects  are,  moreover,  of  the  greatest  commercial  import- 
ance. Take,  for  example,  the  breaking  of  a  high-tension  cable  circuit 
in  air  or  in  oil,  and  trace  out  the  rises  of  potential  in  the  two  cases.  At 
first  sight  one  would  think  the  air-break  would  be  best ;  it  is  not  so,  but 
quite  the  reverse.    What  effect  has  the  air  arc  then  on  the  circuit  ? 

I  wish  now  to  acknowledge  the  very  considerable  help  my  former 
assistant,  Mr.  S.  Blackley,  has  rendered  me  in  connection  with  the 
oscillograms  here  reproduced.  It  has  meant  many  a  night  till  2  or  3 
a.m.,  when  after  a  hard  da/s  work  he  has  given  up  his  spare  time  and 
devoted  himself  to  the  work  with  the  spirit  of  an  enthusiast.  I  wish 
also  to  express  my  indebtedness  to  Dr.  Magnus  Maclean  for  the  help  he 
has  given  me  in  the  preparation  of  this  paper. 

Professor  Professor  Magnus  Maclean*  wished  to  compliment  Mr.  Field  on 

MacEai.  the  excellence  of  his  paper  submitted,  both  from  an  experimental 
and  mathematical  point  of  view.  It  was  a  paper  with  which  he  was 
more  or  less  familiar,  as  Mr.  Field  was  kind  enough  to  show  him 
many  of  the  experiments  some  time  ago,  and  the  theories  put  forward 
and  the  inferences  deduced  were  mutually  discussed  on  several  occa- 
sions. There  were  many  points  in  the  paper  to  which  he  would  like  to 
refer,  but,  as  the  evening  was  far  advanced,  he  would  confine  himself  to 
the  investigation  which  Mr.  Field  gave  to  prove  that  the  nth  and  13th 
harmonics  are  the  most  important.*  The  way  in  which  he  showed  that 
an  nth  and  a  13th  could  be  inferred  from  the  12  ripples  observed  in 
the  direct-current  voltage  was  most  ingenious,  original,  and,  he  thought, 
correct. 

But  he  did  not  think  that  Mr.  Field  was  justified  in  stating  as  he  did 

•  It  would  be  more  in  accordance  with  ordinary  notation  and  nomenclature 
to  call  the  term  containing  a  frequency  eleven  times  the  fundamental  fre- 
quency the  loth  harmonic,  and  to  call  the  term  containing  a  frequency 
thirteen  times  the  fundamental  frequency  the  12th  harmonic.  Thus  with 
frequencies  i,  2,  3,  4,  .  .  etc.,  2  is  the  first  harmonic,  3  the  second 
harmonic,    .    .    .    etc. 


1903.]  DISCUSSION.  695 

that  these  harmonics  are  the  most  important.  As  a  matter  of  fact,  the  Professor 
mathematical  equation  from  which  he  deduced  this  result  was  an  M^San. 
assumed  equation :  and  if  one  assumed  a  corresponding  equation  like 
a  (i  -cos  6  kf),  it  would  follow  by  the  same  reasoning  and  the  same 
nomenclature  that  the  5th  and  the  7th  frequencies  would  be  the  most 
unportant.  To  find  by  the  usual  analysis  whether  lower  harmonics 
were  present  or  not.  Professor  Maclean  got  Mr.  Blackley  to  magnify 
four  of  the  curves  by  means  of  a  pantagraph.  These  magnified  curves 
were  not  very  accurate,  especially  at  the  ripples,  which  were  much 
sharper  than  they  should  be.  This  was  due,  as  Mr.  Blackley  explained 
to  him,  to  a  sticking  of  the  pantagraph.  However,  he  thought  they 
were  accurate  enough  to  enable  him  to  find  if  there  were  terms  contain- 
ing 3  or  5  times  the  fundamental  frequency.  The  enlarged  curves  were 
XV,  XVII,  XX,  and  another  not  given  in  the  paper,  but  similar  to  XXI. 
He  would  call  it  XXI.  He  only  had  time  to  try  the  last  three  mentioned 
curves,  and  these  only  for  frequencies  3,  5,  and  11  times  the  funda- 
mental. As  terms  containing  even  multiples  of  the  fundamental 
frequency  cannot  appear  in  these  curves,  the  general  equation  is  : — 

/•(E)  =  E.  sin  ^/  +  E3  sin  (3  /^/  +  ^3)  +  E5  sin  (5/^/  +  e^)  -j-  .  .  . 
.  .  .  -h  E„sin(ii^/  +  e„)  +  E,3  sin  (13 /►  / -f  e.3)  +  .  .  . 

The  process  of  finding  E,  E3  E5  .  .  .  etc.  is  well  known.  It  simply 
consists  for  finding  Ejin  dividing  the  whole  curve  into  three  equal  parts, 
superimposing  these  three  parts  and  finding  a  third  of  the  resultant 
ordinates  at  each  point  of  the  abscissae.  If  this  is  a  sine  curve,  its 
maximum  ordinate  is  E3.  Again,  to  find  E5,  divide  the  whole  curve  into 
five  equal  parts  ;  superimpose  these  parts  and  find  a  fifth  of  the  algebraic 
sum  of  the  ordinates  at  each  point  of  the  abscissae.  If  this  curve  is  a 
sine  curve  its  maximum  ordinate  is  E5.  The  others,  E^  E,  .  .  .  etc., 
can  be  similarly  dealt  with. 

Due  to  a  fault  in  the  oscillogram,  as  mentioned  in  the  paper  by  Mr. 
Field,  the  distance  o  to  t  is  not  equal  to  the  distance  x  to  2ir.  Hence, 
when  looking  for  frequencies  3  and  5,  he  divided  o  to  tt  into  30  equal 
parts,  and  also  t  to  2x  into  30  equal  parts.  This  gave  him  twenty  read- 
ings for  the  curve  containing  frequency  3,  and  twelve  readings  for  the 
curve  containing  frequency  5.  None  of  the  curves  gave  any  indication 
that  a  frequency  3  was  present,  but  they  all  showed  frequency  $  quite 
pronounced ;  and  considering  the  inaccuracy  of  the  curves  analysed, 
the  curves  obtained  in  each  case  were  fairly  good  sine  curves.  He  now 
tried  for  E„  by  dividing  each  half  of  the  curve  into  33  equal  parts, 
giving  him  6  points  on  the  curve.  All  the  three  curves  showed 
frequency  11  very  good.  He  had  no  time  to  try  for  any  of  the  others. 
The  results  he  obtained  were  in  arbitrary  units  : — 


CuR\^  XVII. 

Curve  XX. 

Cl'Rvk  XXI. 

/(E)„„  =  387 

/(E)_  =  42-0 

/(E)„^  =  34 

E5  „  =  27 

E5    „  =      1-2 

E5  „   =    1-4 

E„  „  =  09 

E„  „  =    1-8 

E„  „  =    4*2 

He  thought  Mr.  Field  was  quite  correct  in  his  main  conclusions  about 
the  nth  and  13th,  but  he  did  not  think  he  was  correct  in  ignoring  the 
Vol.  82.  46 


696        FIELD:  THE   PHENOMENON  OF  RESONANCE.     [Glasgow, 


ProfesstM- 

Magnus 

Maclean. 


Professor 
A.  Jamieson. 


other  harmonics.  Indeed,  in  Curve  XVII.,  the  fourth  harmonic  is 
more  important  than  the  loth,  though  the  reverse  is  the  case  in 
Curve  XXI. 

In  subtracting  the  harmonics  so  found  from  the  original  curve,  it  is 
quite  obvious  that  there  are  more  harmonics  in  each  of  them  than  the 
fourth  and  tenth.  He  believed  from  the  appearance  of  them  that  there 
are  more  harmonics  than  the  fourth,  tenth,  and  twelfth,  but  he  had  had 
no  time  to  work  further  at  the  curves. 

Professor  Andrew  Jamieson  said  that  any  one  who  had  carefully 
studied  such  books  as  "The  Alternate  Current  Transformer  in  Theory 
and  Practice,"  by  Prof.  Fleming,  and  the  second  or  latest  enlarged 
edition  of  "  Alternate  Current  Working,"  by  Prof.  A.  Hay,  the  mathe- 
matical parts  of  Mr.  Field's  paper  were  simple,  clear,  and  explicit 
Since  he  was  dealing  with  actual  concrete  examples,  the  meaning  of 
several  of  the  formulae  were  applied  in  a  more  telling  manner,  than  will 
be  found  in  most  treatises  upon  alternate-current  testing  and  working. 
Mr.  Field  had  explained  by  blackboard  sketches,  in  a  clearer  and  more 
detailed  manner  than  that  stated  in  the  proof  copy  of  his  paper,  the 
principle,  construction,  and  action  of  Duddell's  oscillograph.  He  had 
also  dwelt  upon  its  capabilities  and  shortcomings,  and  pointed  out 
how  he  overcame  some  of  its  defects.  He  might  explain  why  he  did 
not  photograph  the  various  waves  of  E.M.F.  and  current  straight  from 
the  beam  of  light  as  reflected  directly  by  the  mirror  which  is  fixed  to  the 
two  phosphor-bronze  strips  (upon,  say,  a  moving  cinematograph  film) 
instead  of  using  the  reflections  from  a  second  mirror,  vibrated 
synchronously  with  the  first  one,  but  at  right  angles  to  its  axis  ?  Was 
there  no  possibility  of  an  error  arising  from  the  use  of  this  special 
motor  and  two  such  mirrors  ? 

Passing  over  the  points  touched  upon  by  the  previous  speakers,  and 
referring  at  once  to  the  condenser  effect  produced  by  electro-static 
capacity  of  the  underground  main  high-tension  cables,  between  the  power- 
house and  the  sub-stations,  they  found  the  well-known  formula  (7)  so 
familiar  to  submarine  cable  electricians,  viz. : — Current,. C  =  2  ir  «  K  V. 
Then  came  equation  (8),  when  a  current  was  passed  through  a  coil 

having  a  coefficient  of  self-induction  L,  where  current  C  = r  • 

^  2  TT  n  L 

And,  when  these  were  equated  under  the  conditions  stated,  we  got 

Now,  as  to  a  mere  matter  of  history,  he  had  had  the  pleasure  of  con- 
ducting a  series  of  experiments,  not  only  with  Thomson  and  Jenkin*s 
curb-sender,  but  also  with  Count  Sicardi's  curb-signalling  key,  leaks, 
and  other  methods.  The  object  of  these  experiments  was  to  find  out  if 
such  devices  minimised  the  retarding  effects  of  electro-static  capacity, 
and  thereby  increased  the  speeds  of  signalling  through  the  long  sub- 
marine cables  of  the  Eastern  Telegraph  Co.  There,  of  course,  the 
capacity  effects  were  very  much  more  pronounced  than  in  the  case  of  the 
short  main  cables  experimented  upon  by  Mr.  Field,  but  the  frequencies 
and  the  voltages  were  very  much  less.  However,  the  increased  speeds 
so  obtained  by  sending  a  reverse  current  after  each  signalling  current. 


1903.]  DISCUSSION.  697 

although  apparent,  did  not  justify  the  permanent  introduction  of  any  Professor 
of  these  methods,  since  Muirhead's  duplex  system  and  Ben.  Smith's  A- J^*"**®*'"* 
manual  translation,  which  came  to  the  front  about  the  same  time — viz., 
1876  to  1878 — showed  better  commercial  results.*  Then  came  Prof. 
S.  P.  Thompson's  proposal  to  introduce  into  the  cable  circuit,  at  stated 
intervals,  a  certain  anti-capacity  effect  by  means  of  self-induction  coils. 
His  idea  consisted  of  arranging  and  fixing  these  coils  to  the  cable 
conductor,  so  that  their  self-induction  should  exactly  or  partially  cancel 
the  electro-static  capacity  effects  of  the  cable.  But  this  bold  proposal 
did  not  meet  with  the  approbation  of  practical  cable  engineers  and 
electricians,  owing  to  the  mechanical  difficulties  of  lowering  such  water- 
tight coils  to  the  bottom  of  the  ocean  whilst  paying-out  the  cable,  and 
of  maintaining  them  in  good  electrical  condition.  He  thought,  however, 
that  this  plan  could  be  successfully  applied  to  long  subterranean  tele- 
graph, telephone,  alternate-current  lighting,  or  power  transmission 
cables.  Mr.  Field  had  shown  how  capacity  and  self-induction  might  be 
so  joined  and  adjusted,  that  the  opposition  to  the  current  was  merely 
like  that  of  a  true  ohmic  resistance.  But,  then,  his  subterranean 
cables  were  easily  got  at ;  and  if  ever  the  "  resonance  effect "  should 
prove  troublesome,  or  from  prior  investigation  of  the  conditions 
should  appear  to  be  in  any  way  dangerous,  the  land  electrician  could 
easily  make  suitable  provision  against  the  same. 

It  was  a  pity  that  Mr.  Field  was  leaving  Glasgow,  because  if  he  had 
continued  his  experiments  with  the  oscillograph  and  tried  it  directly  at 
the  central  station,  the  Section  would  in  all  probability  have  either  had  a 
fresh  paper  or  an  appendix  to  his  present  long  and  weighty  one, 
stating  whether  or  not  the  capacity  of  even  two-  or  three-mile 
lengths  of  the  Glasgow  tramway  mains,  between  the  central  power- 
house and  any  of  the  sub-stations,  did  appreciably  tone  down  the 
wave  forms,  as  illustrated  in  the  diagrams  placed  before  us.  He 
(Professor  Jamieson)  thought  the  author  had  said,  that  he  had  not  come 
across  a  case  wherein  the  resonance  effect  had  proved  dangerous  to 
such  cables.  He  was  under  the  impression  that  the  first  subterranean 
cables  put  down  at  Londonderry,  had  been  punctured  or  their  insula- 
tion resistance  seriously  diminished  by  some  such  action.  With  such 
a  splendid  field  for  research,  he  hoped  that  the  Glasgow  Tramways' 

•  [I  think  that  electricians  who  have  opportunities  of  experimenting  upon 
long  submarine  cables  or  artificial  lines  should  carefully  study  Mr.  Field's 
paper,  as  well  as  the  experiments  by  F.  Dolezatek  and  A.  Ebelinz  on  the 
"  Pupin  System"  of  long-distance  telephony  (see  Electrician^  April  and  March, 
1903).  They  should  then  try  and  devise  the  simplest  and  best  combination  of 
oscillograph  and  cinematograph  for  delineating  the  curves  of  charging  and 
discharging  or  of  signalling  and  of  receiving  currents,  under  a  great  variety  of 
conditions.  They  could  vary  the  internal  resistance  and  E.M.F.  of  their 
sending  batteries,  the  resistance  and  sensitiveness  of  their  receiving  instru- 
ments, the  capacities  of  their  sending  and  receiving  condensers,  the  periods 
of  curbing  currents,  the  effects  of  introducing  "  Pupin  Coils,"  etc.  By  trying 
and  systematically  comparing  the  photographic  curves  derived  from  these 
various  changes  upon  cables  of  different  lengths  with  different  ratios  of 
capacity  and  resistance  per  naut,  they  would  have  a  much  more  searching 
and  surer  means  of  arriving  at  correct  views  upon  the  possibilities  of 
increasing  speeds  of  signalling,  than  by  any  of  the  older  methods  hitherto 
adopted.— A.  Jamieson.J 


698        FIELD:  THE  PHENOMENON  OF  RESONANCE.    [Glasgow, 

PiofMsor  oscillograph  would  not  be  allowed  to  rest  in  its  instrument  case,  but 
A.jamic»oii.  ^^^  .^  ^.^j^^  ^  ^^jj  further  skilfully  applied  to  investigations  such 
as  had  now  been  suggested.  It  could  not  be  placed  in  better  hands 
than  one  or  other  or  both  of  the  previous  speakers,  who  would  un- 
doubtedly start  fair  and  square  at  once  at  the  very  fountain-head, 
where  only  the  full  pressures  of  6,500  volts  were  to  be  found  I  They 
must  not,  however,  forget  to  earth  the  centre  or  neutral  point  of  the 
armature  ;  for  it  would  be  very  sad  to  have  to  mourn  their  "  loss." 

At  page  681,  Mr.  Field  says,  "  We  are  now  getting  into  the  range  of 
the  wireless  telegraphist."  But,  surely,  one  of  the  principal  objects  of 
the  tramway  or  lighting  electrical  engineer  is  to  keep  as  far  as  possible 
away  from  such  a  range  of  voltage  and  frequency,  when  dealing  with 
dielectrics  that  would  be  sure  to  suffer  from  these  effects.  One  of  the 
chief  difficulties  which  Mr.  Marconi  had  to  surmount,  was  to  ascertain 
how  best  to  arrange  and  proportion  the  values  of  his  induction  coils 
and  condensers,  ithat  for  a  given  primary  power  he  might  obtain 
the  most  effective  electrical  "  splashes "  across  his  "  spark-gap." 
Both  Marconi  and  his  colleagues  had  made  many  calculations  and 
experiments,  and  he  understood  that  he  required  at  Poldhu  Station  a 
steam  engine  of  not  less  than  150  B.H.P.  to  generate  his  sending 
currents.  This  was,  however,  a  mere  nothing  to  the  more  powerful 
Pinkston  engines ;  but  happily  their  currents  and  circuits  were  not 
similarly  directed  and  arranged,  or  we  should  have  wireless  waves 
sent  right  round  the  earth  ! 
Ml.  Hird.  Mr.  W.  B.  Bird  said  :  The  practical  uses  to  which  the  oscillo- 

graph might  be  put  have  been  strikingly  brought  out  in  this  paper, 
and  in  this  connection  there  was  one  point  specially  noticeable. 
Mr.  Field  mentioned  that  he  was  unable  to  obtain  good  curves  when 
the  conditions  of  the  circuit  were  such  as  to  produce  resonance 
and  give  great  amplitude  of  the  harmonics  he  was  observing,  because 
the  oscillograph  motor  under  these  conditions  fell  out  of  step.  Some 
years  ago  he  had  worked  with  a  very  rough  oscillograph ;  the  curves 
were  obtained  by  passing  the  currents  to  be  observed  through  long 
wires  stretched  in  a  magnetic  field,  and  carrying  mirrors,  the  beam  of 
light  from  which  was  thrown,  not  as  in  the  present  instrument  on  a 
vibrating,  but  on  a  rotating,  mirror.  The  curve  was  thus  drawn  out  in 
a  long  trace,  and  by  working  in  a  dark  room  a  photograph  could  easily 
and  simply  be  obtained  on  a  sensitive  plate  or  strip  of  bromide  paper. 
As  many  of  the  phenomena  which  it  would  be  most  interesting  to 
observe  were  obtained  under  conditions  which  were  likely  to  throw  the 
oscillograph  motor  out  of  step,  it  would  appear  that  some  such 
method  of  doing  away  with  the  synchronous  motor  would  have  some 
advantages.  Whilst  quite  agreeing  with  Mr.  Field  that  a  12th  or  any 
even  harmonic  is  inadmissible  in  curves  obtained  from  the  generators^ 
he  described,  because  it  would  make  the  positive  and  negative  halves  of 
the  curves  dissimilar,  he  saw  no  reason  why  such  a  machine  should  not 
produce  current  curves  in  which  the  right  and  left  halves  of  each  half- 
period  were  unsymmetrical,  and  he  therefore  did  not  sec  that  the  fact 
that  an  even  harmonic  would  produce  such  want  of  symmetry  could  be 
quoted  as  an  additional  reason  for  the  absence  of  such  harmonics. 


1903.J  DISCUSSION.  699 

Mr.  Field,  after  giving  his  very  ingenious  explanation  of  how  the  nth  Mf-**^"*- 
and  13th  harmonics  in  each  of  the  three  phases  combine  to  give  12 
ripples  in  the  D.C.  curve,  said  that  no  other  pair  would  combine  in  the 
same  way  ;  it  seemed,  however,  that  the  5th  and  7th  harmonics,  if 
present  in  each  of  the  three  phases,  would  combine  to  form  6  ripples, 
and  the  17th  and  19th  to  form  18  ripples,  in  exactly  the  same  way, 
and  using  the  same  reasoning  as  that  by  which  it  is  shown  that  the 
nth  and  13th  combine  to  give  12  ripples.  It  would  be  extremely 
interesting  to  examine  the  D.C.  curves,  and  to  attempt  to  increase  the 
amplitude  of  these  harmonics,  say,  by  resonance,  so  as  to  detect  either 
6  or  18  ripples  in  the  curve  ;  and  if  such  were  discovered,  this  would 
be  a  striking  confirmation  of  Mr.  Field's  theory  of  the  genesis  of  these 
ripples. 

Mr.  S.  Blackley  said  :  After  such  a  lengthy  paper,  it  was  very  Mr. 
difficult  to  add  anything  further  to  try  to  satiate  the  desire  for  informa-  ^  ' 
tion  on  this  interesting  subject,  as  Mr.  Field  has  suggested  that  he 
should  do.  Resonance  was  a  most  fascinating  property  of  the  electric 
circuit,  and  the  importance  of  its  effects  on  alternating-current  systems 
was  frequently  under-estimated,  if  at  all  considered.  It  was  usually 
stated  that,  in  practice,  the  danger  accruing  from  resonance  was  a 
myth,  or  that,  no  bad  effects  having  resulted  so  far,  the  system  under 
consideration  was  immune  from  danger  of  this  kind.  When  they 
considered  that  the  insulation  of  our  electrical  plant  and  cables  must 
be  deteriorating  to  a  certain  extent  as  time  goes  on,  and  remembered 
that  in  a  high-tension  system,  consisting,  say,  of  transformers,  induction 
motors,  and  perhaps  fifty  or  sixty  miles  of  good  capacity-giving  cable, 
the  resonating  combinations  which  might  occur  are  numerous,  they 
should  keep  in  mind  the  possibility  of  trouble  from  resonance  effects. 
He  should  reconmiend  any  one  who  was  inclined  to  be  sceptical  on  this 
question  to  endeavour  to  obtain  a  glimpse  of  the  effects  (as  shown  by 
an  oscillograph)  which  a  resonating  harmonic  of  even  a  moderate 
frequency  had  on  the  E.M.F.  wave  of  an  alternator  on  ho  load,  or  to 
watch  the  arc  formed  on  opening  a  high-tension  air-break  switch  in 
the  circuit  in  which  resonance  existed.  On  switching  on  a  few  high- 
tension  feeders  he  had  seen  the  13th  harmonic  in  Curve  XX.  resonate 
to  such  an  extent  that  all  semblance  to  the  original  wave  form  had 
disappeared,  and  slightly  undulated  sinusoidal  wave  of  great  amplitude 
and  of  a  periodicity  of  325  cycles  per  second  had  taken  its  place.  The 
question  naturally  occurred — What  would  happen  if  they  had  a  small 
polyphase  synchronous  motor  running  light  on  this  circuit  when  these 
cables  were  switched  on  ?  Would  the  motor,  with  its  field  not  too 
strongly  excited,  prefer  to  stand  still  or  to  speed  up  to  synchronism  at 
the  higher  frequency  ?  In  either  case,  if  they  had  no  previous  knowledge 
of  what  was  going  on  in  the  circuit,  he  expected  that  the  result  would  be 
attributed  to  the  speed  variation  of  the  engine.  Previous  to  Mr.  Field's 
experiments  he  had  frequently  noticed,  but  could  not  account  for,  the 
sparking  which  was  exhibited  all  over  the  high-tension  feeder  circuit- 
breakers  in  the  sub-stations  as  the  main  engine  was  starting  up  in  the 
morning  or  slowing  down  at  night.  This  sparking  seemed  to  be  statical 
in  nature,  and  occurred  between  the  woodwork  and  iron  fittings  of  the 


700        FIELD  :  THE   PHENOMENON   OF  RESONANCE.      [Glasgow, 


Mr. 
lilacklcv. 


Dr.  J.  B. 
Henderson. 


circuit-breakers.  On  investigation  it  was  found  that  the  phenomenon 
always  appeared  and  disappeared  at  a  certain  voltage,  lower  than  the 
normal,  as  indicated  by  the  high-tension  voltmeter  in  the  sub-station, 
the  needle  of  the  instrument  remaining  stationary  for  a  few  seconds 
while  the  sparking  lasted.'^*-  Immediately  after  the  sparking  had  ceased 
the  voltage  began  to  rise  gradually,  and  nothing  further  was  noticed • 
They  then  examined  the  E.M.F.  wave  by  means  of  the  oscillograph  as 
the  voltage  fell  at  night,  and  found  that  sparking  commenced  when 
the  main  engine  reached  a  speed  such  that  the  frequency  correspond- 
ing was  of  a  value  suitable  to  produce  resonance  of  one  of  the 
harmonics  in  the  wave.  The  wave  form  was  very  similar  to  that 
shown  in  Curve  XV^.  From  a  consideration  of  the  formula  for 
resonance,  viz.,  i  =  4  tt*  «"  K  L,  the  above  result  would  be  expected. 
Since  adopting  Mr.  Field's  suggestion  as  to  starting  up  or  shutting 
down  on  the  high-tension  side  the  sparking  had  disappeared, 
except  at  the  normal  voltage  of  6,500,  and  only  then  when  a  certain 
length  of  cable  was  in  circuit.  On  page  667  Mr.  Field  referred  to  the 
method  of  arriving  at  the  capacity  of  the  cables  by  measuring  the 
charging  current  flowing  into  them.  Perhaps  it  would  be  vnsc  to 
explain  that  they  only  expected  to  arrive  at  an  approximate  value  of  the 
capacity  by  the  method  indicated.  The  inconsistency  in  the  results 
was  largely  due  to  the  fact  that  the  E.M.F.  wave  of  the  alternator  was 
not  sufficiently  near  the  sinusoid  in  form  to  admit  of  the  use  of  the 
formula  C  =  2  irn  V  K/io^  The  results  served,  however,  to  show  how 
utterly  unreliable  this  method  of  determination  of  capacity  was  even  for 
approximations.  It  was  well-known  that  the  capacity  current  would  be 
a  minimum  when  the  alternator  used  gave  a  pure  sine  wave.  In  a  later 
test,  which  he  had  not  had  an  opportunity  to  confirm,  he  measured  the 
current  flowing  into  the  cables  when  the  capacity  was  such  as  to  give 
t^e  conditions  indicated  by  Curve  XX.  and  again  under  conditions  of 
more  pronounced  resonance  than  in  Curve  XV.  Strangely  enough,  the 
results  were  only  consistent  if,  in  the  former  case,  they  calculated  the 
capacity  using  25  as  the  value  of  the  frequency,  while  in  the  latter 
the  frequency  is  Jaken  as  13  by  25.  The  capacity  values  determined 
only  vary  by  3  per  cent.,  the  higher  value  going  with  the  higher 
frequency. 

Dr.  J.  B.  Henderson  said  that  Mr.  Field  assumed  that  the  ripples  on 
the  alternator  E.M.F.  wave  consisted  of  sine  curves  superposed  on  the 
fundamental.  This  might  not  represent  the  facts  in  every  case,  but  it 
was  an  assumption  as  justifiable  as  that  the  E.M.F.  curves  of  our  old 
alternators  were  sine  curves,  and  it  might  lead  to  some  important  general 
conclusions.  Working  on  this  assumption,  he  had  calculated  the 
harmonics,  up  to  the  29th,  which  were  present  in  the  ripples  shown  in 
Figs.  7  and  8.  Mr.  Field  had  already  calculated  some  of  those  present 
in  Fig.  7,  but  it  was  Fig.  8  which  represented  the  E.M.F.  curve  of  each 
phase  winding  of  the  alternator.  The  ripples,  however,  which  Mr. 
Field  traced  by  means  of  the  oscillograph  were  the  ripples  on  the  line 
E.M.F.  curve,  and  as  the  alternator  windings  were  connected  in  star, 

•  The  voltmeter  used  was  of  a  type  which  would  not  read  correctly  at  all 
frequencies. 


1903.]  DISCUSSION.  701 

they  were  the  ripples  which  resulted  from  combining  two  of  the  curves,  Dr.  j.  b. 
like  Fig.  8,  at  6o°  phase  difference.  If  we  represented  the  amplitudes  "<^°*^<^»^n- 
of  the  ripples  in  Fig.  8  by  i,  2,  2,  2,  2,  i,  the  amplitudes  of  the 
ripples  in  the  resultant  wave  were  i,  3,  4,  4,  3,  i.  It  was  interesting  to 
notice  that  all  harmonics  which  were  multiples  of  3  disappeared  by  a 
combination  in  star  and  were  magnified  by  a  combination  in  mesh,  so 
that  they  would  cause  currents  to  circulate  in  the  delta.  The  accom- 
panying table  gave  the  values  of  the  harmonics  up  to  the  29th  in  the 
three  cases  which  he  had  mentioned.  It  would  be  noted  from  the  last 
column  that  on  the  line  wires  the  harmonics  11  and  13  were  more  than 
thirty  times  as  important  as  any  of  the  others,  except,  of  course,  the 
first,  which  S3mchronised  with  the  fundamental,  and  was  therefore  of 
no  account  in  our  comparison.  Professor  Maclean  was,  he  understood, 
analysing  some  of  the  actual  oscillograms  taken  by  Mr.  Field.  If 
his  analysis  did  not  agree  with  the  last  column  it  simply  proved  that 
the  sine  curve  assumption  was  wrong  for  this  particular  alternator.  In 
analysing  these  ripples  he  presumed  that  Professor  Maclean  had,  first 
of  all,  corrected  the  curves  for  the  errors  of  the  oscillograph  which 
Mr.  Field  mentioned  in  the  paper,  as  the  inequality  in  the  horizontal 
scale  of  the  oscillogram  would  introduce  much  more  serious  errors  in 
the  analysis  for  the  higher  harmonics  than  for  the  lower. 

When  we  considered  the  combination  of  three  similar  line  E.M.F.'s 
in  mesh  connection  as  in  the  rotary  converter  armature,  the  harmonics 
also  combined  at  phase  differences  which  depended  on  the  particular 
harmonic  considered.  The  phase  difference  in  the  n^  harmonic  was 
n  X  120".  We  found  then  that  the  harmonics  i,  7,  13,  i9i  25,  etc.,  com- 
bined at  -h  120°  phase,  while  the  harmonics  5,  11,  17,  23,  etc.,  combined 
at  —  120°  phase.  If  therefore  the  fundamentals  gave  a  rotating  field  in 
one  direction,  the  harmonics  7, 13, 19,  25,  etc.,  would  give  rotating  fields 
in  the  same  direction,  and  the  fields  due  to  the  harmonics  5,  11,  17,  23 
would  rotate  in  the  opposite  direction.  The  speed  of  field  rotation  was, 
of  course,  proportional  to  the  frequency.  By  reasoning  similar  to  that 
used  by  Mr.  Field  for  the  nth  and  13th  harmonics  applied  to  the  rotary 
converter,  we  saw  that  there  would  be  ripples  on  the  direct-current 
E.M.F.  of  the  rotary  having  6,  12,  18,  24,  etc.,  waves  per  period  of  the 
alternating  current.  Since  these  were  all  even  harmonics,  the  direct- 
current  curve  should  always  be  a  smooth  curve,  no  matter  how  angular 
the  E.M.F.  cur\'e  on  the  alternating  side  might  be  with  its  odd  har- 
monics. The  D.C.  Curves  III.,  X.,  and  XI.  were  a  strong  confirmation 
of  the  much  greater  intensity  of  the  nth  and  13th  harmonics  than  of 
any  of  the  other  harmonics  in  the  A.C.  E.M.F.,  and  these  curves  there- 
fore tended  to  confirm  the  figures  given  in  column  14  of  the  above  table. 
He  had  to  thank  Mr.  Field  for  giving  him  the  opportunity  of  discussing 
this  excellent  paper,  in  which  he  felt  a  great  interest,  as  he  had  con- 
versed with  him  from  time  to  time  about  the  work,  and  had  been 
privileged  to  watch  the  actual  changes  taking  place  in  the  E.M.F. 
waves  as  the  cable  system  was  altered. 


702 


FIELD  :  THE    PHENOMENON    OF   RESONANCE.      [Glasgow, 


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1903]  DISCUSSION.  703 

Professor  A.  Gray  said  that  he  had  read  Mr.  Field's  paper  with  P«>f.Gray. 
much  interest,  and  regarded  it  as  an  example  of  the  benefit  to  be 
derived  from  a  free  use  of  Mr.  Duddell's  beautiful  instrument.  When 
once  the  curves  had  been  thus  drawn,  the  well-known  methods  of  har- 
monic analysis  could  be  at  once  applied  to  separate  out  the  harmonics 
which  existed  in  the  wave  forms,  and  thus  to  exhibit  the  fundamental 
components  of  the  action  of  the  machines.  This  was  a  further  step  of 
some  importance,  and  perhaps  some  of  the  mechanical  analysers  which 
had  been  devised  for  periodic  curves  might  be  made  use  of  in  this  con- 
nection. It  was  only  by  such  registration  of  the  behaviour  of  machines 
and  subsequent  analysis  that  w^e  could  obtain  light  upon  the  various 
matters  which  were  still  obscure  in  the  action  of  generators  of  different 
kinds.  He  had  felt  specially  interested  in  the  discussion  on  resonance, 
and  in  that  part  of  the  paper  dealing  with  the  alternating  charge  and 
discharge  of  cables.  The  curves,  though  small  in  scale  and  therefore 
difficult  to  examine  closely,  were  almost  surprisingly  identical  with  the 
cur\'es  that  one  could  draw  for  the  oscillatory  subsidence  of  the  charge 
of  a  condenser  from  the  theoretical  equation,  obtained  by  supposing  the 
plates  connected  by  a  coil  of  definite  unvarying  self-inductance.  The 
crests  of  the  successive  ripples  lay  on  the  exponential  curve  {e,g,,  Figs. 
24,  26,  etc.,  if  it  was  that  these  had  been  drawn  for  actual  cases  by 
discharge  through  the  inductive  coils  of  a  machine)  which  one  would 
have  expected  in  such  a  case.  Now,  the  self-inductance  of  the  circuit 
cquld  not  be  constant  in  this  case,  but  must  be  some  function  of  the 
current,  and  therefore  of  the  time ;  and  the  exact  solution  of  the 
differential  equation  could  not  be  given  unless  this  function  was  known, 
and  almost  certainly  only  by  approximation  even  then.  He  would  Hke 
to  see  a  large  scale  of  curves  for  this  case.  In  the  meantime,  it  was 
interesting  to  have  the  results  given  in  the  paper.  The  fact  that  the 
potential  on  a  cable  at  charge  or  at  discharge  might  be  very  much 
greater  than  the  working  j)otential  was,  of  course,  a  result  that  might 
have  been  anticipated  without  experiment,  but  Mr.  Field's  exhibition 
of  it  in  this  way  must  be  of  great  value  to  practical  men  in  calling 
attention  to  the  matter,  and  in  causing  those  in  charge  of  plant  of  this 
description  to  realise  the  danger  that  probably  had  not  occurred  to 
anybody. 

There  were  a  good  many  corrections  required  in  the  proof,  which 
would  no  doubt  be  made  by  the  author,  and  he  did  not  desire  to  make 
these  in  any  way  a  matter  of  criticism.  But  some  of  the  more  mathe- 
matical slips  should  be  carefully  scrutinised.  There  were  some  points 
in  connection  with  the  curves  which  he  had  not  yet  had  time  to 
consider,  which  he  should  like  to  go  into  at  some  future  time — for 
example,  as  to  curves  XXXVI.,  which  were  very  interesting.! 

The  only  other  remark  he  would  make  at  present  was  as  to  the 
definition  of  self-inductance.  There  were  two  definitions  current ;  one 
was  the  equation 

E=RC  +  L^ (0 

in  which  it  denoted  the  coefficient  of  the  time  rate  of  variation  of  the 
current  dCldi  in  the  expression  for  the  electromotive  force  in  the 


704        FIELD;  THE  PHENOMENON  OF   RESONANCE.       [Glasgow, 

Prof.  Gray,  circuit.  In  a  circuit  containing  iron,  of  course,  L  was  not  a  constant,  but 
was  the  rate  of  variation  d  N/d  C  of  the  total  number  N  of  lines  of  force 
through  the  circuit  with  variation  of  the  current  C.  This  definition  had, 
no  doubt,  its  advantages  for  dynamo  work,  otherwise  practical  men 
would  not  employ  it,  and  he  was  not  to  be  taken  as  objecting  to  it.  But 
there  was  the  other  sense  in  which  the  term  self -inductance  had  been 
employed  by  most  of  the  pioneers  in  electro-magnetic  theory  ;  the 
defining  equation  was  here 

N  =  LC (2) 

where  N  had  the  same  meaning  as  before,  L  was  not  here  a  constant 
either,  and  its  relation  to  the  L  of  the  former  equation  was  easily  exhi- 
bited.   We  had  clearly  from  the  equation  just  written 

rf  N  _        rfN  dQ 
dt   —  '*  dC   di 


\    ^     dd  dt 


by  (2),  so  that  if  we  denoted  the  L  defined  by  equation  (i),  that  is 
d  ^jd  C  by  L',  and  use  L  for  the  quantity  defined  by  equation  (2),  we 
had— 

L'=  L  +  C  -'^^. 
d  C 

The  difference  was  that  V  united  in  one  symbol  the  two  parts  of  the 
coefficient  of  d  Cjd  t  in  the  equation  of  electromotive  force  (i) ;  and  the 
two  values  coincided  in  the  case  of  constant  self-inductance.  As  he  had 
indicated,  there  was  this  double  use  of  the  term  self-inductance,  which 
was,  he  thought,  a  pity.  One  definition  was  as  directly  applicable  to 
alternating  circuits  as  the  other  ;  the  important  thing  to  remember  in 
either  case  was  that  when  there  was  iron  present  the  self-inductance 
was  variable.  The  matter  was  entirely  one  of  definition,  and  in  that 
the  convenience  of  all  concerned  should,  of  course,  be  consulted. 

Perhaps  it  was  unnecessary,  but  there  was  no  warning  given,  so  far 
as  he  could  see,  that  the  whole  mathematical  disquisition  commencing 
on  page  677  to  near  the  end  proceeded  on  the  assumption  that  L  was 
constant,  which,  of  course,  it  was  far  from  being  in  the  circuits  of  the 
machines  usually  employed  in  the  work  referred  to. 

The  paper  represented  a  vast  amount  of  good  work,  though  in  its 
present  uncorrected  form  its  complete  perusal  was  a  matter  of  consider- 
able difficulty.  He  hoped  that  it  would  be  printed,  so  that  its  results 
might  be  fully  understood  and  appreciated. 


1903.]  TRANSFERS,  DONATIONS  TO    LIBRARY,    ETC.  705 


The  Three  Hundred  and  Ninetieth  Ordinary  General 
Meeting  of  the  Institution  was  held  at  the  Institution 
of  Civil  Engineers,  Great  George  Street,  Westminster, 
on  Thursday  evening,  March  12th,  1903 — Mr.  James 
Swinburne,  President,  in  the  chair. 

The  minutes  of  the  Ordinary  General  Meeting  of  February  26th, 
1903*  were,  by  permission  of  the  Meeting,  taken  as  read  and  signed  by 
the  President. 

The  names  of  new  candidates  for  election  into  the  Institution  were 
also  taken  as  read,  and  it  was  ordered  that  their  names  should  be 
suspended  in  the  Library. 

The  following  list  of  transfers  was  published  as  having  been 
approved  by  the  Council  : — 

From  the  class  of  Associate  Members  to  that  of  Members — 

Ralph  Henry  Govern  ton. 

From  the  class  of  Associates  to  that  of  Associate  Members — 

Alfred  S.  L.  Barnes  |        Andrew  Stewart. 

George  Richard  Drummond.        t        E.  Taylor. 
Richard  Christopher  Simpson.      |        H.  Osborn  Wraith. 
Warwick  Makinson. 

From  the  class  of  Students  to  that  of  Associates- 
Harold  Thomas  Brown.  |      Frederick  Edward  Kennard. 
Cuthbert  John  Greene. 

Messrs.  Quin  and  Speight  were  appointed  scrutineers  of  the  ballot 
for  the  election  of  new  members. 

Donations  to  the  Library  were  announced  as  having  been  received 
since  the  last  meeting  from  the  Italian  Ambassador ;  to  the  Building 
Fund  from  Messrs.  R.  C.  Barker,  J.  R.  Bedford,  W.  J.  Bishop,  R.  H. 
Burnham,  A.  D.  Constable,  R.  A.  Dawbarn,  F.  W.  E.  Edgcumbe, 
W.  Fennell,  A.  G.  Hansard,  E.  R.  Harvey,  C.  E.  Hodgkin,  G.  F.  R. 
Jacomb-Hood,  Lord  Kelvin,  H.  Kilgour,  H.  Lea,  A.  E.  Levins, 
F.  H.  Nicholson,  M.  Robinson,  H.  Seward,  F.  W.  Topping,  C.  E.  Wigg, 
and  A.  P.  Whitehead  ;  and  to  the  Benevolent  Fund  from  Messrs.  W.  J. 
Bishop,  R.  V.  Boyle,  M.  S.  Chambers,  K.  W.  E.  Edgcumbe,  J.  W. 
Fletcher,  Prof.  R.  T.  Glazebrook,  E.  P.  Harvey,  A.  E.  Levin, 
M.  Robinson,  A.  P.  Trotter,  H.  J.  Wagg,  and  R.  W.  Weekes,  to  whom 
the  thanks  of  the  meeting  were  duly  accorded. 


706        WIRING  RULES— TELEGRAPH  CONFERENCE.     [March  12th, 

The  President  :  It  will  be  within  the  knowledge  of  many  of  the 
members  that  the  Council  has  been  engaged  for  some  time  past  in  the 
preparation  of  Wiring  Rules.  A  committee  has  sat  and  worked  very 
hard  in  connection  with  the  subject,  and  we  have  now  drafted  a  set  (^ 
Wiring  Rules,  which  have  been  passed  by  the  Council,  having  first 
been  dealt  with  word  by  word  by  a  very  large  and  representative 
Committee.  The  Wiring  Rules  have  been  submitted  to  the  Incor- 
porated Municipal  Electrical  Association,  which,  after  making  some 
slight  alterations  and  improvements,  has  adopted  them.  That  body 
had  a  representative  on  the  Committee.  Several  of  the  largest  Fire 
Insurance  Companies  have  also  adopted  the  Rules.  The  Wiring  Rules 
at  present  issued  by  different  bodies  are  not  only  divergent,  but  in 
some  cases  incompatible  with  the  new  set  of  Rules  as  drawn  up  by  this 
Institution.  We  hope  that  our  Rules  will  gradually  supersede  others,- 
and  introduce  uniformity  in  standardisation.  It  is  proposed  to  send 
them  to  supply  engineers,  consulting  engineers  and  the  Power 
Companies  and  contractors,  and  it  is  hoped  that  members  will  use 
every  possible  effort  to  get  the  Rules  adopted,  and  will  use  them 
themselves  whenever  they  possibly  can,  and  so  gradually  get  them 
introduced  universally.  A  Standing  Committee  has  been  appointed,  so' 
that  if  any  alterations  arise  from  time  to  time  they  can  be  dealt  with  as 
they  arise.  It  will  not  be  necessary  to  wait  until  there  is  any  very 
large  improvement  needed.  Any  small  alterations  can  be  made 
practically  at  once  if  it  is  found  necessary. 

There  is  another  matter  which  has  been  before  the  Council  for  some 
time  to  which  I  desire  to  draw  attention,  namely,  that  a  Telegraph 
Conference  is  to  be  held  in  England  in  May  or  June  of  this  year. 
Most  of  us  in  our  days  come  to  listen  to  papers  in  this  Institution 
which  are  not  Telegraph  papers,  but  we  must  remember  that 
Telegraphy  was  the  original  work  of  this  Institution.  We  were 
originally  a  telegraph  society,  and  although  we  do  not  now  get  so 
many  papers  and  novelties  on  the  subject  of  telegraph  work,  telegraphy 
is  by  no  means  correspondingly  unimportant.  In  fact,  it  is  the  other 
way  about ;  telegraphy  has  got  to  such  a  high  pitch  of  perfection  that 
there  is  very  little  to  bring  forward  before  the  Society.  Telegraphy  is 
of  enormous  importance  to  this  Institution.  I  may  remind  you  that 
this  Congress  is  an  International  affair,  and  will  be  a  very  large  and 
important  gathering  ;  the  Council  therefore  feels  that  we  ought  to  do 
everything  we  can  to  entertain  the  Congress,  and  to  take  our  proper 
part  in  the  proceedings.  But  a  difficulty  at  once  occurs,  because  it 
will  be  held  at  the  end  of  one  session  and  the  beginning  of  the  next. 
The  Council  feels,  and  has  felt  all  along,  that  the  right  thing  to  do  is  to 
have  one  President  to  take  charge  of  the  Institution  over  that  time,  and 
to  have  a  President  selected  for  that  purpose.  There  is  one  man  in 
particular  who  is  exactly  the  right  man  to  be  President  under  those 
circumstances,  and  I  have  little  doubt  the  Council  will  select  him.  In 
order  that  the  Council  may  have  the  opportunity  of  selecting  a 
President,  and  of  his  being  elected  so  as  to  preside  during  the 
Congress,  and  to  give  him  ample  time  to  make  the  needful  prepara- 
tions, I  propose  to  send  in  my  own  resignation  between  this  and  the 


1903.]     CONSTABLE  &  FAWSSETT :  DISTRIBUTION  LOSSES.      707 

next  meeting.  Then,  by  the  Regulations,  the  Council  will  be  able  to 
nominate  their  own  new  President,  who  will  take  charge  on  that  election 
until  the  General  Meeting.  After  the  General  Meeting,  of  course,  the 
President  has  to  be  nominated  and  elected  in  the  usual  way  by  the 
Institution ;  but  when  you  know  whom  the  Council  proposes  as 
President  I  know  you  will  be  unanimous  in  electing  him  for  the 
following  year  also. 

I  will  now  call  on  Mr.  Fawssett  to  read  the  paper  which  he  has 
written  together  with  Mr.  Constable.  It  is  most  unfortunate  that  Mr. 
Constable  is  very  seriously  ill.  He  was  not  able  to  be  here  on  the  last 
occasion,  and  he  is  not  able  to  be  here  to-night,  but  we  hope  very 
much  he  will  be  able  to  be  present  at  the  next  meeting,  and  give  him 
our  best  sympathies. 


DISTRIBUTION    LOSSES    IN    ELECTRIC    SUPPLY 

SYSTEMS. 

By  A.  D.  Constable,  Associate-Member,  and 
E.   Fawssett,  Associate. 

"  Dare  quant  accipereJ*  This  is  a  motto  not  universally  followed  by 
electrical  engineers  in  the  course  of  their  business,  yet  in  the  case  of  a 
particular  supply- station  of  quite  moderate  capacity,  over  800  tons  of 
coal  are  annually  given  gratis  to  warm  up  the  town,  and  the  authorities, 
besides  not  receiving  one  penny  towards  the  cost  of  it,  do  not  even 
receive  the  thanks  of  the  residents  for  the  grateful  warmth  provided. 

Few  central  "station  engineers  expect  to  get  paid  for  more  than 
75  per  cent,  of  the  energy  they  generate.  Of  the  remaining  25  per 
cent,  about  four-fifths  is  absolutely  wasted ;  and  worse  than  that,  it 
increases  the  waste  which  would  otherwise  take  place.  The  other 
fifth  is  used  in  the  station  itself  for  lighting  and  other  purposes,  and 
cannot  be  said  to  be  actually  wasted,  although  it  is  unproductive  as 
regards  revenue. 

It  is  worth  while  considering  how  this  wasted  20  per  cent,  is  made 
up,  and  whether  it  is  possible  to  reduce  it  in  any  way,  since  it  costs  as 
much  to  generate  each  unit  wasted  as  each  unit  sold. 

The  figures  given  in  this  paper  refer  to  the  Croydon  Electricity 
Works. 

The  total  losses  incurred  between  the  generator  terminals  and  the 
consumers'  terminals,  leaving  out  of  consideration  the  units  used  in 
the  station  for  field  excitation,  lighting  and  driving  auxiliaries,  may  be 
subdivided  under  the  following  five  headings  : — 
(i)  Losses  in  Switchboards  and  Connections. 

(2)  Losses  in  High  Pressure  Feeders. 

(3)  Losses  in  Transformers. 

(4)  Losses  in  Low  Pressure  Cables. 

(5)  Losses  in  Meters. 

These  are  discussed  under  the  various  headings,  Nos.  2  and  4  being 
taken  together. 


708         CONSTABLE  AND  FAWSSETT  :  DISTRIBUTION     [Mar.  12th, 

Switchboard  Losses. 

Notwithstanding  the  fact  that  we  are  not  dealing  with  a  material 
substance  like  gas,  which  has  to  be  conveyed  through  pipes  with 
innumerable  possibilities  of  leakage,  there  is  an  actual  loss  in  trans- 
mitting electrical  energy  to  the  consumers  of  over  20  per  cent,  of  the 
total  energy  sent  out  of  the  station. 

The  actual  loss  by  leakage  is  extremely  small ;  by  far  the  larger 
part  is,  of  course,  due  to  our  having  no  perfect  conductors  at  our 
disposal,  and  this  loss  due  to  conductor  resistance  is  infinitely  more 
important  than  the  corresponding  loss  of  pressure  due  to  pipe  friction. 


TABLE  No.  I. 
Losses  Up  To  axd  Including  Main  Switchboard. 


1 

S>'stem  of  Supply. 

Maximum  Output. 

Approximate  Mean  Loss 

in  per  cent,  of  Annual 

Output. 

, 

2,000     volts    alt. 

I     ' 

cur.    one    pole 
earthed. 

500  volts    direct 

[      1,250  K.W. 
) 

0-43 

'{ 

cur.  Tramways 
(A) 

500  volts    direct 

V        500  K.W. 

0-42 

3     ] 

cur.  Tramways 
(B) 

t        400  K.W. 

0-30 

Average  loss  in  Substation  Switchgear  (System  i)  and  connections  : 
o'lo  per  cent,  of  output. 

It  becomes  appreciable  even  at  the  feeder  terminals  on  the  main 
switchboard.  Table  I.  gives  these  initial  losses  in  the  case  of  three 
different  sets  of  plant.  The  values  were  obtained  by  measurement, 
and  may  be  taken  as  a  very  fair  average  of  the  usual  existing  con- 
ditions. Careful  arrangement  of  the  relative  positions  of  the  switch- 
board and  generators  and  simple  design  of  the  switchboard  will,  to 
some  extent,  eliminate  these  losses. 

The  minimum  number  of  instruments  should  be  installed,  and  these 
should  be  connected  with  as  few  joints  as  possible ;  ammeters  should 
preferably  be  of  the  shunted  type.  Some  switchboard  erectors  have  a 
natural  incapacity  for  screwing  connections  up  tight,  and  some  instru- 
ment makers  are  afraid  of  giving  their  customers  too  much  metal ;  the 
authors  have  come  across  several  cases  of  joints  which  have  welded 
themselves  together,  of  bus-bars  running  at  or  over  200°  F.,  and  even 
of  switch-gear  working  at  a  temperature  of  150°  F.  at  normal  full  load. 

One  square  foot  of  dull  copper  surface  running  at  10"  F.  above  the 
temperature  of  the  air  will  continuously  dissipate  the  heat  produced  by 


1903.]  LOSSES  IN  ELECTRIC  SUPPLY  SYSTEMS.  709 

the  absorption  of  about  i6  watts,  or,  if  the  excess  temperature  is  50°  F. 
the  watts  will  be  about  60. 

Main  fuses  should  be  avoided  where  possible,  not  only  because  they 
■  are  objectionable  in  themselves,  but  to  be  of  use  they  must  run  warm 
and  consequently  waste  energy. 

It  may  be  said  that  these  are  refinements  beneath  the  notice  of  the 
practical  engineer,  but  in  the  station  under  consideration,  which  is  of 
fairly  modern  design  with  an  output  of  only  1,250  k.w.  at  the  maximum, 
the  total  loss  per  annum  in  the  switch-gear  and  connections  alone 
(including  those  in  the  substation)  amount  to  10,000  units,  which,  it 
will  be  readily  granted,  shows  considerable  room  for  improvement. 

In  those  cases  where  the  generator  pressure  is  raised  before  trans- 
mission, in  addition  to  the  switchboard  losses  there  are  those  in  the 
step-up  transformers  to  be  taken  into  consideration  ;  these  are  dealt 
with  in  the  section  on  transformer  losses  later  on. 

Cable  Losses. 

Of  all  the  losses  in  the  system,  the  cable  losses  are  the  most 
important  and  those  that  can  be  least  easily  reduced.  The  larger  part 
of  this  paper  will,  therefore,  be  devoted  to  their  consideration. 

The  total  losses  in  the  cables  may  be  split  up  into  three  com- 
ponents : — 

(i)  CR  losses  in  the  dielectric. 

(2)  CR  losses  in  the  conductor. 

(3)  Losses  due  to  what  may  be  called  dielectric  hysteresis. 

The  first  may  be  shortly  dismissed ;  it  is,  as  stated  above,  generally 
very  small,  at  any  rate  in  the  main  feeders  of  a  well  laid  out  system. 

The  total  insulation  resistance  between  poles  of  this  system  of 
2,000-volt  feeders,  comprising  about  25  miles  of  concentric  cable  in 
nine  separate  feeders  (ranging  from  '150''  to  '0250")  was  o'lo-^, 
including  switchboards  at  both  ends.  This,  at  a  pressure  of  2,000  volts, 
corresponds  to  a  total  leakage  current  of  0*02  ampere,  or  a  loss  of  only 
40  watts,  or  350  units  per  annum,  i.e.,  14  units  per  mile  of  high-tension 
cable. 

The  insulation  of  the  low-tension  network  is,  of  course,  very  much 
less,  and  can,  with  difficulty,  be  measured ;  if  we  include  all  switch- 
gear,  network  boxes,  and  services,  it  may  be  about  1,000  w  for  50 
miles  of  cable,  and  at  200  volts  the  lost  watts  will  be  again  40,  or  7 
units  per  mile  of  cable  per  annum.  The  50  miles  of  low-tension  cable 
roughly  correspond  to  the  25  miles  of  high-tension  cable,  so  that  the 
total  leakage  loss  is  only  700  units  per  annum. 

The  above  figures  give  a  rough  idea  of  what  may  be  expected  in 
this  direction,  and  it  is  useless  to  go  into  greater  detail,  owing  to  the 
enormous  variations  of  insulation  met  with  in  practice.  The  insulation 
of  a  low-tension  network  may  be  of  the  order  of  ohms  without  being 
detected,  for  a  long  time.  A  case  in  a  neighbouring  system  once  came 
under  the  authors'  notice  in  which  there  was  a  leak  sufficient  to  raise 
a  mass  of  concrete  round  a  bunch  of  cables  to  a  red  heat  before  it  was 
noticed  ;  this  is,  happily,  a  very  exceptional  case. 


710        CONSTABLE  AND   FAWSSETT  :  DISTRIBUTION     [Mar.  12lh, 

The  second  cause  of  loss,  viz.,  that  due  to  C*R  in  the  cables,  is  of 
the  greatest  importance,  and  it  also  lends  itself,  in  the  case  of  feeders 
at  least,  to  fairly  accurate  calculation.  In  the  case  of  the  low- tension 
network,  however,  the  loss  can  only  be  approximately  ascertained. 

Table  II.  gives  the  C'R  losses  for  the  whole  of  the  Croydon  system 
of  mains.  They  have  been  worked  out  for  each  quarter  of  the  year, 
the  basis  of  the  calculation  being  the  load  curves  shown  in  Diagram 
No.  I.  The  upper  full  curve  is  the  load  curve  for  a  December 
week-day.  The  lower  curve  is  the  load  for  a  day  in  July,  and  the 
middle  curve  is  the  mean  for  September  and  March.  The  curve  for 
March  is  rather  higher  than  that  for  Septembei^  owing  no  doubt  to  the 
latter  being  the  holiday  season.  In  working  out  the  losses,  these 
curves  have  been  assumed  to  be  the  mean  curves  for  the  corresponding 
quarter,  and  the  current  in  each  separate  feeder  and  distributor  has 
been  assumed  to  follow  the  same  law  as  the  total  current. 


TABLE  No.  II. 

CR  Losses  in  Cables. 

Maximum  Load  Supplied  :  1,250  K.W. 


Description  of  Cables. 

CaR  T/>ss  in  Units  per 

Annum. 

2,000  volt   Feeders  and  Sub-feeders.    About 
25    miles,  0*15  sq.   inch  section    to  0025 
sq.  inch           

400    and  200  volt    Distributors.      About   50 
miles,  040  sq.  inch  section  to  o'lo  sq.  inch 

H.T.  Arc  Cables,   io*6  miles,  0*023  sq.  inch 
Section  (series)           

L.T.  Arc  Cables.  About  20  miles,  006  sq.  inch 
and  0*025  sq.  inch  section 

Total 

47,200 

66,200 

IMOO 

25,800 
150,600 

This  is,  of  course,  not  strictly  accurate,  but  is  near  enough  for  the 
purpose  of  this  calculation.  An  exception  has  been  made  in  the  case 
of  the  public  lighting  load,  as  this,  of  course,  follows  a  different  law. 
The  lower  dotted  lines  in  the  diagram  are  the  load  curves  for  public 
lighting,  and  are  calculated  from  Diagram  No.  II.  as  a  basis,  there 
being  in  this  case  a  total  of  400  arc-lamps,  180  of  which  are  switched 
off  at  about  midnight.  The  greater  part  of  these  lamps  are  fed  in 
parallel  at  200  volts  alternating,  from  low-tension  mains  used  for  no 
other  purpose. 


1908.] 


LOSSES   IN   ELECTRIC  SUPPLY  SYSTEMS. 


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712        CONSTABLE  AND   FAWSSETT  :  DISTRIBUTION    [Mar.  1^ 

These  mains,  however,  take  their  supply  from  the  same  low-tension 
bus-bars  in  the  substations  as  the  private  supply.  There  are  in  addition 
four  high-tension  series  circuits  supplying  together  134  lamps. 

The  upper  dotted  curves  are  the  private  lighting  load  curves  for  the 
respective  quarters,  and  are  used  to  calculate  the  C'R  losses  in  the  low- 
tension  network,  in  conjunction  with  the  observed  average  drop  in 
potential  between  the  substations  and  consumers'  terminals,  which 
latter  averages  four  or  five  volts. 

We  now  pass  on  to  the  third  heading — "  Losses  due  to  dielectric 
hysteresis,"  to  use  the  term  for  want  of  a  better  one.  After  the  very 
thorough  way  in  which  this  question  was  discussed  recently  before  this 
Institution,  perhaps  an  apology  is  needed  for  again  bringing  up  the 
subject.  As  the  question  was  not  finally  settled,  it  was  the  intention  of 
the  authors  to  experiment  thoroughly  on  the  large  system  of  high- 

HOURS  or    PUBLIC  UCHTINC 


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Diagram  No.  II. 


tension  cables  at  Croydon,  and  find  out  once  for  all  what  the  true 
losses  incurred  in  actual  working  were ;  an  additional  incentive  was  the 
desire  to  again  demonstrate  that,  contrary  to  the  usual  belief,  it  was 
possible  in  certain  cases  to  obtain  a  power-factor  as  high  as  o'lo  in  a 
cable,  as  was  stated  to  be  the  case  in  Mr.  Mordey's  paper  and  in 
Mr.  Minshall's  contribution  to  the  discussion  thereon.  The  latter  is 
conclusively  proved  by  the  figures  in  Table  IV. 

The  more  ambitious  scheme  was  doomed  to  partial  disappointment 
at  any  rate ;  it  has  been  found  a  task  of  very  great  difl&culty  to  obtain 
these  losses  with  any  reasonable  accuracy  with  the  instruments  available 
in  a  fairly  well  equipped  test-room.  Numerous  experiments  have 
been  made,  but  owing  to  the  interruptions  due  to  the  necessary  routine 
of  work  of  a  central  station  in  an  exceptionally  busy  year,  these  results 
are  somewhat  meagre  and  inconclusive.  This  section  of  the  paper  is, 
therefore,  rather  of  the  nature  of  a  series  of  suggestions,  and  it  is  hoped 
that  the  discussion  will  produce  further  data. 


1908.] 


LOSSES  IN   ELECTRIC   SUPPLY  SYSTEMS. 


713 


The  experiments  are  here  discussed  seriatim,  as  some  of  the 
methods  adopted  and  the  difficulties  experienced,  as  well  as  the  few 
results  obtained,  may  be  of  interest. 

The  methods  available  for  this  investigation  are  : — 
(i)  Direct  measurement  of  watts  used  in  the  cable  by  a  wattmeter 
either  with  or  without  a  choker  to  improve  the  power-factor 
of  the  circuit. 

(2)  Calculation  of  watts  from  plotted  curves  of  volts  and  current 

or  from  oscillograph  records. 

(3)  Direct  measurement  of  increased  power  necessary  to  drive  an 

alternator  when  a  cable  is  switched  on. 

(4)  Calorimetric  method,  i.e.,  measurement  of  rise  of  teipperature 

due  to  lost  watts. 

(5)  Calculation  of  watts  lost  from  known  data  and  law  of  current 

variation  determined  experimentally. 

ZJDOO     VOLT         BUS -BAR 


Earth         bar. 
Diagram  No.  III. 


The  first  three  methods  have  been  used  in  this  investigation  with 
the  results  discussed  below.  Method  (4)  is  one  difficult  of  application 
and  impossible  in  the  case  of  cables  in  the  ground,  and  is  in  any  case 
open  to  many  sources  of  error. 

Method  (5)  has  not  been  attempted,  as  sufficient  data  as  to  the  law 
of  current  variation  have  not  been  obtained. 

With  regard  to  method  (i),  the  first  thing  necessary  was  to  discover 
what  reliance  could  be  placed  on  the  readings  of  the  ordinary  com- 
mercial wattmeters  at  our  disposal,  when  used  on  various  power- 
factors. 

Three  wattmeters  were  used,  viz.  (i)  a  Swinburne  with  no  unneces- 
sary metal  parts.  This  wattmeter  had  three  different  sets  of  current 
coils  to  give  different  sensibilities.  (2)  and  (3)  Thomson  inclined  coil 
wattmeters  of  different  ranges  with  frames  partly  of  metal.  All  three 
had  large  non-inductive  resistances  in  series  with  the  pressure  coil,  and 
were  wound  for  250  volts. 


714        CONSTABLE  AND  FAWSSETT  :  DISTRIBUTION    [Mar.  12th, 

TABLE  No.  III. 
Wattmeter  Constants. 


Date. 


17-7-01 


4-8-01 
6-8-01 

17-8-01 
6-8-01 


17-8-01 

4-8-01 

17-8-01 
8-901 


10-9-01 

4-8-01 

7-8.01 
6-9-01 

4-8-01 
6-9-OI 

6-901 
17-8-01 


Nature  of  Load. 


Non-inductive  Lamp 
bank 

do. 

do. 

do. 

do. 

do. 

do. 

do. 

do. 
Inductive,     Current 
leading 

da 

do. 

do. 
Do..  Cur.  lagging   .. 

do. 

do. 

do. 
Do.,  Cur.  leading    .. 

do. 

do. 

do. 

Do.,  Cur.  lagging  .. 

Do.,  Cur.  leading   . . 

Non-inductive  lamp 

bank 


THOMSON    WATTMETER 


Power 
Factor. 


Con- 
sUnt. 


Scale 
Rdgs. 


Voltage 
Curve 
similar 
to 


SWINBURNE    WATTMETER. 


No.  10 

Sheet 

A. 

12.  St  B. 

1N0.  10 
Sheet 
A. 

No.  10 
•  Sheet 
A. 
No.  la 
Sheet  a 
No.  10 
Sheet  A. 


No.  10 

Sheet 

A. 

la.St.  B. 

10,  St  A. 


roo 

992 

15 

100 

1005 

21 

i-oo 

983 

30 

x-00 
100 

9-90 

9-88 

t 

1*00 

9*93 

14 

I -00 

9^ 

15 

i-oo 

lo-ox 

23 

I -00 

9^ 

39 

o-iag 

9*03 

25 

0-374 

9-98 

61 

0*141 

10-20 

5 

0143 

IO-I7 

3 

0033 

V^ 

2 

0304 

16 

0034 

10-26 

2*5 

O-03S 

10-90 

a-5 

0-129 

1-262 

M 

0-129 

1195 

30 

0-143 

1-256 

as 

0-142 

1193 

45 

0-034 
0-I38 

0952 

25 

1-189 

35 

X-000 

1-278 

70-90 

AMP.    RANGE. 


Non-Inductive  Lamp 
Bank 

do. 

do. 
Induc-Cur.  leading 

do. 
Do.,  Cur.  lagging 

do. 

da 


»p 

I'OO 

1-027 

140    { 

I-oo 

100 

60-140  J 

100 

1-063 

140 

0-I4I 

1-016 

30 

0-I4I 

1-040 

50 

0-032 

1-271 

13 

0-304 

1*026 

150 

0035 

1-015 

22 

.  No.  12 
Sheet  B. 
No.  10 
Sheet 

A. 

No.  12 

Sheet  B. 

la  St.  A. 


THOMSON    WATTMETER.    10    AMP.    RANGE. 

Non-inductive  Lamp 

Bank         ..  1*00 

do.  . .  1*00 

Inductive,     Current 

leading  . .  0*142 

do.  . .  0143 

Do.,  Cur.  lagging   . .  0*035 


978 

21 

9*96 

37 

No.  10. 
Sheet 

6-60 

35 

•     A. 

7-81 

6 

. 

8-83 

3 

/ 

Remarks. 


Original  Fme  Wire  , 
Current    CoU. 
about   No.    16 
S.W.G. 


Current  Coil  re- 
wotmd  with  fine 
vrire,  about  No. 
26.    S.W.G. 

Cur.  C<ril  rewound 
as  above,andal»o 
new  vc^colL 


As  used  in  all  ex- 
periments after 

4-8-01. 


Not  used  owing 
to  variable  con- 
stant 


The  voltage  was  reduced  in  the  ratio  of  about  10  :  i  by  means  of  a 
bank  of  lamps,  the  actual  ratio  being  measured  for  each  set  of  readings ; 
the  voltage  on  the  wattmeter  was  measured  on  a  standard  electrostatic 
instrument,  and  the  full  voltage  was  reduced  by  a  transformer  of  known 
ratio  and  measured  on  the  same  voltmeter. 

Diagram  No.  III.  shows  the  connections  for  calibrating  the  watt- 
meters initially  ;  it  is  almost  self-explanatory,  and  power-factors  of 
about  0-03  and  0-35  with  current  lagging,  0*14  with  current  leading, 
and  unity  were  used  in  the  calibration.    The  leading  current  was 


1908.] 


LOSSES   IN  ELECTRIC  SUPPLY  SYSTEMS. 


715 


obtained  by  passing  a  current  through  the  series  coil  of  the  wattmeter 
in  phase  with  the  applied  volts  and  connecting  the  pressure  coil  to  a 
non-inductive  resistance  in  series  with  a  choker.  The  wattmeter  is 
§hown  connected  in  this  way  in  the  diagram. 

The  power-factor  of  the  ironless  choker  circuit  of  course  can  be 
calculated  with  very  fair  accuracy.  The  choker,  as  used  throughout, 
consisted  of  112  lbs.  of  No.  16  copper  wire  wound  on  a  wooden  drum. 
A  thermometer  was  embedded  in  the  winding  and  the  temperature  was 
taken  for  each  reading. 

The  resistance,  in  series  with  the  choker,  consisted  of  lamps.  It 
has  been  assumed  throughout  that  the  lamp  banks  used  were  non- 
inductive,  no  difference  in  phase  between  current  and  applied  volts 
being  observable  on  the  oscillograph  used  in  these  experiments. 

Table  III.  gives  the  constants  obtained  for  the  wattmeters  under 
the  various  conditions. 


2.000  VOLT    BUS- BAR 


0 

0 


]n([]  NN'   tWi#i#iJ 


Diagram  No.  IV. 


It  will  be  noticed  that  the  Swinburne  Wattmeter  and  the  small 
range  Thomson  Wattmeter  give  fairly  consistent  results,  although  there 
are  considerable  variations  with  the  different  power-factors,  chiefly 
due,  in  all  probability,  to  the  various  wave-forms  of  the  applied  voltage. 
There  are  also  variations  in  the  constant  obtained  under  the  same 
conditions  at  different  times,  but  as  the  constant  used  in  working  out 
the  cable  watts  was  that  obtained  under  the  most  nearly  corresponding 
conditions,  and  at  the  same  time  in  most  cases,  the  errors  should  not  be 
large.  Very  low  power-factors  with  leading  current  were  not  obtain- 
able for  calibration  owing  to  the  lack  of  a  larger  choker. 

In  the  case  of  the  larger  range  Thomson  instrument  the  constants 
vary  from  6*6  to  nearly  lo'o,  notwithstanding  the  maker's  statement 
that  the  instrument  is  correct  for  all  power-factors  and  all  wave-forms  ; 
this  apparently  applies  between  certain  limits  only.  The  readings  of 
this  instrument  were,  therefore,  rejected.    In  the  later  experiments  by 


716        CONSTABLE  AND   FAWSSETT :  DISTRIBUTION    [Mar.  12th, 

a  slight  modification  of  the  connections  it  was  possible  to  calibrate  the 
wattmeter,  in  use,  on  a  load  with  leading  current,  for  every  reading, 
and  this  was  done  in  each  case. 

The  actual  connections  used  in  the  cable  experiments  are  shown  in 
Diagram  No.  IV.,  two  wattmeters  being  generally  used  in  series  as  a 
check. 

Readings  were  taken,  both  with  and  without  the  choker  C  in 
parallel  with  the  cable. 

L  in  the  diagram  is  a  bank  of  lamps,  used  in  the  earlier  experi- 
ments in  calibrating  the  wattmeters  with  PF  =  i.  The  ammeters 
were  all  compared  with  a  low-reading  Siemens  Dynamometer,  but 
the  final  standard  was  an  Elliott's  Voltmeter,  used  in  conjunction 
with  a  standard  ohm. 

The  arrangement  on  the  right  of  the  diagram  at  the  bottom  is  for 
the  purpose  of  calibrating  the  oscillograph.  A  voltage  of  130  D.C. 
could  be  applied  to  the  oscillograph  without  altering  the  connections 
and  the  value  of  the  deflection  in  volts  thus  obtained. 

In  the  same  way  a  known  direct  current  could  be  passed  through 
the  non-inductive  current  shunt  R,  and  the  value  of  the  oscillograph 
deflection  in  amperes  ascertained. 

The  principal  results  obtained  are  given  in  Table  IV.,  and  the 
agreement  of  the  watts  absorbed  in  the  cable  as  measured  by  the 
wattmeters  and  by  working  out  the  oscillograph  curve,  is  in  some 
cases  good.  These  curves  were  worked  out  by  taking  the  mean  value 
of  the  instantaneous  watts  for  22,  and  in  some  cases  44,  equi-distant 
points  of  time  in  the  diagram  of  one  complete  period. 

In  several  instances  it  will  be  noticed  that  the  R.M.S.  value  of  the 
voltage  obtained  from  the  oscillograph  diagrams  is  higher  than  that 
measured  on  the  voltmeter.  This  is  probably  due  to  the  fact  that  the 
calibration  was  made  with  130  volts  instead  of  200  volts,  and  the  re- 
sistance of  the  lamps  in  series  with  the  voltage  strip  was  higher  than  it 
was  in  the  actual  experiment,  thus  making  the  oscillograph  appear  less 
sensitive  than  it  really  was. 

In  the  case  of  Experiment  No.  15  and  onwards  this  possible  error 
did  not  occur,  as  there  were  no  lamps  in  series  with  the  voltage  strip, 
and  the  agreement  is  better,  though  in  this  case  the  voltage  as  measured 
is  slightly  higher  than  that  obtained  by  working  out  the  curves. 

The  watts  taken  by  the  choker  alone  have  been  also  worked  out 
from  the  oscillograph  curves  (Curves  D),  and  the  agreement  with  the 
calculated  watts  is  in  this  case  good. 

Some  experiments  had  to  be  made  without  the  oscillograph,  owing 
to  its  being  out  of  order,  so  that  in  these  cases  the  watts  are  only  those 
obtained  on  the  wattmeter.  Some  were  made  without  a  wattmeter 
and  some  without  independently  calibrating  the  oscillograph  (see  last 
column  in  Table  IV.).  In  the  four  cases  in  which  watts  have  been 
obtained,  both  from  the  oscillograph  records  and  with  a  wattmeter, 
the  two  values  are  of  the  same  order,  but  they  do  not  agree  as  well  as 
could  be  wished. 

This  is,  no  doubt,  explained  partly  by  the  shape  of  the  waves.  In 
curves  of  shapes  E,  F,  and  G,  for  example,  owing  to  the  almost  vertical- 


Exp. 

Date  of 

Cable 

No. 

Experiment. 

No. 

I 

21-7-OI 

4 

2 

8-9-OI 

4 

3 

8-cH)l     j 

4 

4 

I4-7-OI     i 

7 

5 

2I-7-OI      i 

7 

6 

4-8-OI 

7 

7 

2I-7-OI 

7 

8 

4-8-OI 

7 

9 

4-8-01     1 

9 

10   1 

8-9-OI 

9 

11 

8-9-01 

9 

12 

8-9-OI 

10 

13 

8-9-OI 

10 

'•♦  . 

4-«-!^*'ctr 

15 

-I0-02 

i6 

-I0-O2      1 

17 

-I0-02      1 

i8 

-7-02 

19 

.7-02     ! 

20 

-7-02 

21 

-10-02 

12 

— 

— 

— 

Description. 


Cone,  jute  insulated,  lead- 
sheathed,  armoured,  direct 
in  ground 
'  Cone.  V.B.  insulated,  laid 
solid  in  iron  trough  with 
iron  eover,  designed  for 
5,000  volts,  worked  at 
2,000  volts 

Cone,  jute  insulated,  V.B. 
sheathed,  laid  solid  in  wood 
trough  with  No.  10 

Cone,  paper  ins.  V.B.S.,  laid 
solid  in  iron  trough  with 
tile  eover,  W.P.  5,000  v. 

112  lb.  No.  16  S.W.G.,  eop-  [ 
per  ;  wound  without  iron  j 

Coneent.    paper    insulation  \ 
V.B.S.,  laid  solid  in  iron  [ 
trough    with    tile    eover,  !• 
working     pressure    5,000 
volts  J 


See  Note  (i.)  at  foot 


Length. 
Yards. 


2,100 


7,290 


2,440 


2400 


6,340 


21,660 


Notes:— (i.)  Cable  No.  12  consisted  01*  Cables  Nos.  9,  13 

type  as  No.  10. 
(ii.)  Worked  out  result  of  Curves  E,  F,  and  G  pi 
(iii.)  Thomson  wattmeter  used  in  series  with  Swii 
(iv.)  No  wattmeter  used  in  E.xperiments  15  to  21. 
(v.)  The  Swinburne  wattmeter  with  original   fine 

Nos.  2,  3,  10,  II,  12,  13. 


Bl.^'S- 


.by^%VaU«^y      OsciUo- 
and -vsTattmeiet 
tcr.  ^ 


grapb- 


fWattmeter    ™ 


74 
lO 
520 
520 

,600 
,110 
5,205 
2,230 
2,090    \ 

1,535    1 
i,3»o    ; 

5i56o    , 

18,740 

I3t530 

1,920 

25,650 

12,000 

3,970 
12,160 


30 
49 
25 
635 
830 
866 

834 

923 

58 


66 

53 

112 

33 
Calc. 

17» 


610, 

83fi 
7* 


0*020 
•029 
•017 
•098 
112 
126 
•112 
•130 
•023 
•030 
•025 

•073 
024 

Oilc. 
•032 


0090 

no 
•033 


•0315 
0127 

•0175 

•0106 

•083 

•080 

•078 

•074 


Corre«ponding 
Curves. 


Applied  volts 
as  Curve  12, 
Sheet  B 
1 1  Current  wave 
/      not  taken 
B 
As  Exp.  5 
A 
C 

f  Applied  volts 
i-  as  Curve  12, 
I    Sheet  B 


E 
F 
G 

I 


L 
H 


Remarks. 


Ironless  choker  in  parallel 
Cable  alone 
Choker  in  parallel 


Cable  alone 


Choker  in  parallel 
Cable  alone 
Choker  in  parallel 

Ironless  choker,  no  cable 

Oscillograph  voltage  strip 
only  calibrated.  Watts 
worked   out  from    curves 

-  and  the  measured  R.M;S. 
values  of  voltage  and  cur- 
rent. For  I,  J,  and  K 
neither  strip  was  calibrated 

Sine  curves  equivalent  to  E 


=^1,650  y^same  type  as  No.  9,  and  No.  13  =  1,640  yards  of  same 


aU.    >^o.  14 

Sw\t\bume,  w^^num  variation  of  10  per  cent. 


^  and  9' 


U 


was  ws<coil  rewound  with  No.  26  S.W.G.  wire  in  Experiments 


^ci 


LOSSES  IN  ELECTRIC  SUPPLY  SYSTEMS.  717 

i  peaks,  it  is  impossible  to  work  out  the  watts  even  with  approxi- 
'  accuracy.    A  horizontal  difference  of  'oi  inch  in  the  relative 
on  of  one  of  the  peaks  of  the  curves  of  current  and  volts  will 
alter  the  power-factor  indicated. 

it  had  been  possible  to  obtain  photographic  records  some  im- 
nent  in  accuracy  would  have  resulted,  but  as  it  is,  with  curves 
by  hand,  very  little  reliance  can  be  placed  on  the  worked  out 
er-factor  of  the  very  peaked  waves. 

)n  the  other  hand,  simpler  wave-forms  can  be  worked  out  fairly 
rately;  Curve  D  for  example.  Referring  again  to  the  table,  it 
be  noticed  that  very  great  discrepancies  occur  between  various 
of  readings  on  the  same  cable  and  also  between  the  results 
ined  with  the  choker  in  parallel  with  the  cable  and  without  it. 
former  results  should  be  the  more  accurate,  owing  to  the  higher 
jwer-factor. 

I  Such  figures  are  not  very  conclusive,  but  they  have  been  obtained 
hh  all  proper  precautions,  and  it  is  hoped  that  some  explanations  of 
le  discrepancies  may  be  suggested. 

Part  of  the  differences  may  be  due  to  the  effect  of  alteration 
f  wave-form  (i)  on  the  actual  losses,  and  (2)  on  the  instrument 
kiications. 

J    It  has  not   been  definitely  proved  whether  the  power-factor  of  a 

ble  is  altered  by  alteration  of  the  wave-form  of  the  applied  voltage, 

not    On  the  whole,  it  may  be  inferred  that  it  is  altered  to  some 

tent,  but  not  largely.    With  wave-forms  as  in  curves  E,  F  and  G,  the 

wer-factor  for  a  long  paper-insulated  cable  comes  out  at  about  0*014 

Lveraging  the  three,  and  with  curves  H,  I  and  J  for  the  same  cable  and 

approximately  the  same  voltage  it  is  o'o8.   A  wattmeter  was  not  used  in 

this  case. 

This  enormous  difference  canpot  be  put  down  wholly  to  the 
difference  of  wave-form,  but  is  most  probably  due  to  the  inaccuracy  in 
working  out  the  very  peaked  waves  of  the  first  set  of  curves,  and  the 
agreement  of  the  three  is  probably  more  coincidence  than  anything 
else.  The  value  obtained  from  the  la^t  three  curves  has  been  taken  as 
the  more  probably  correct. 

With  regard  to  the  effect  of  wave-form  on  the  other  instruments 
used,  it  is  stated  by  Benischke  that  there  may  be  a  difference  of  10 
per  cent,  in  the  readings  of  electromagnetic  instruments  with  flat  and 
peaked  waves. 

In  calibrating  the  various  instruments  used,  differences  amounting 
to  about  5  per  cent,  were  found  when  using  different  wave-forms, 
the  sub-standard  being  a  Siemens  Dynamometer  with  practically'  no 
metal  parts  in  the  frame,  and  this  should  read  sensibly  the  same  for 
different  wave-forms  and  frequencies.  The  Thomson  Ammeters  read 
higher  on  the  smoother  waves.  In  working  out  the  experiments  the 
calibration  with  the  particular  wave-form  of  the  experiment  was  that 
used.  In  Table  III.,  giving  the  wattmeter  constants  obtained  at 
different  times,  the  form  of  wave  is  noted  for  each  set  of  readings. 
It  was  found  that  the  voltage  across  the  terminals  of  the  current 
coil  of  the  Swinburne  Wattmeter  (using  the  fine  wire  coil)  varied  in  the 


718        CONSTABLE   AND   FAWSSETT :  DISTRIBUTION     [Mar.  12th, 

ratio  of  about  i  :  3  in  the  various  experiments  owing  to  the  difference 
in  the  current  frequency. 

It  is  difficult  to  say  to  what  extent  a  wattmeter  may  be  relied  on 
when  the  current  has  about  double  the  frequency  of  the  applied 
voltage. 

In  order  to  overcome  the  difficulty  of  very  small  scale  readings  on 
the  wattmeters,  the  current  coils  were  in  most  cases  heavily  overrun,  a 
short-circuiting  switch  being  put  in  except  when  taking  readings. 

It  is  interesting  to  note  that  in  one  experiment,  not  recorded  in  the 
table,  the  wattmeter  gave  a  higher  reading  when  short-circuited  than 
when  the  current  coil  was  in  circuit,  no  doubt  due  to  currents  induced 
by  the  voltage  coil,  which  was  in  circuit. 

In  all  the  recorded  experiments  the  measuring  .instruments  were 
placed  in  the  earthed  outer  of  the  cables,  as  it  was  found  that  the 
readings  were  practically  identical  with  those  obtained  vvith  the  in- 
struments on  the  inner,  and  the  safety  of  the  arrangement  was  much 
greater. 

It  was  considered  a  matter  of  interest  to  find  out  how  the  wave- 
forms and  values  of  current  and  voltage,  varied  at  different  points  in 
the  length  of  a  cable,  if  at  all.  An  experiment  was,  therefore,  made  as 
follows : — 

Six  long  cables  were  joined  in  series,  and  readings  of  current  and 
voltage  and  tracings  of  the  wave-forms  were  taken  at  each  end  and  at 
the  junction  of  the  two  middle  cables.  Four  ends  being  accessible  at 
the  power-station,  it  was  not  necessary  to  move  the  oscillograph  at  all. 

The  readings  taken  at  the  end  at  which  the  voltage  was  applied  are 
recorded  in  Experiment  No.  12,  Table  IV.,  as  are  also  the  lengths  and 
sections  of  the  various  cables. 

The  results  of  this  particular  test  showed  that,  contrary  to  the 
authors'  expectations,  there  was  no  observable  difference,  either  in 
the  voltage,  or  in  the  wave-forms  of  the  voltage  and  current  at  the 
three  points.  The  middle  point  was  at  the  junction  of  Cables 
Nos.   10  and  11. 

The  current,  of  course,  had  different  values  at  the  three  points,  but 
whether  it  and  the  watts  were  in  proportion  to  the  equivalent  length  of 
cable  cannot  be  stated  with  certainty,  as  the  cables  are  of  different 
types  and  sizes;  the  main  point,  however,  is  that  there  is  no  change 
in  the  voltage  at  the  ends  of  the  cable  or  in  the  shapes  and  relative 
phases  of  the  voltage  and  current  waves. 

This  experiment  was  made  under  different  conditions :  (i)  with  the 
cable  open-circuited  at  the  far  end,  and  (2)  with  a  small  non-inductive 
load  at  the  end.  The  results  were  the  same  in  both  cases  except  for 
a  very  slight  reduction  in  the  "kinks"  in  the  voltage  curves  in  the 
latter  case  and  a  slight  shifting  of  the  current  wave  owing  to  the  higher 
power-factor. 

The  result  is  the  more  remarkable  as  it  is  the  generally  accepted 
view  that  in  all  long  cables  there  is  a  rise  of  pressure  due  to  the 
capacity ;  and,  under  certain  conditions,  this  does  undoubtedly  take 
place.  In  all  probability  a  variation  of  frequency  would  have  produced 
the  result  expected. 


^£W 


rjoji^ 


^  YORK 

BRARY 


fELNOX 

OATI0N8. 


FORMS   IN    CABLKS, 
(See  Tahle  IV.) 


^ 

^ 

V 

\ 

t 

y 

\    i 

■   1^ 

y 

kf 

^    1 

r 

1    . 

\    1 

/iv 

/ 1 

V 

— - 

fhv  s;^1nt*»  iH'   ''^^^'  ''^  '^'^''^^ 


1903.] 


LOSSES  IN   ELECTRIC  SUPPLY  SYSTEMS. 


719 


It  is  unnecessary  to  show  the  curves  obtained  at  the  three  points,  as 
they  are  all  practically  alike. 

The  actual  readings  obtained  are  given  in  Table  No.  IV  a. 

TABLE  No.  IV  A. 
Variation  of  Current  and  Volts  along  Cable. 


Volts. 

Current 

Volt 
Amperes. 

Watts  by 
OsciUograph. 

901 
1> 

Cable  on  (  Point  A  (near  end) 

open     <  Point  B    (middle) 

Circuit.      Point  C    (far  end) 

Small      (Point  A 

load      <  Point  B 

at  end.     (  Point  C 

2,000 
2,000 
2,000 

2,000 
2,000 
2,000 

6-o8 

3*97 
0 

565 
375 
0-64 

12,160 

7,940 

0 

11,300 
7,500 
1,280 

A  wattmeter  was  not  used  in  this  experiment,  and  the  oscillograph 
curves  for  the  first  reading  only  have  been  worked  out. 

The  current  and  voltage  curves  in  the  last  case  are  identical. 

In  addition  to  the  above  experiments,  it  was  sought  to  confirm  the 
results  by  the  motor  alternator  method.  The  connections  of  the  D.C. 
motor  were  as  shown  in  Diagram  No.  V.,  the  current  being  measured 


®- 


iT'X/ )   (motor) 


Diagram  No.  V. 

by  a  very  sensitive  differential  method,  which  is  clearly  shown  in  the 
diagram.  The  galvanometer  was  calibrated  by  adding  a  small  known 
cmrent  to  the  motor  current  and  noting  the  scale  deflection  ;  the  scale 
was  a  proportional  one. 

Whilst  this  method  was  applicable  to  the  V.B.  cable,  giving  the  watts 


720        CONSTABLE  AND  FAWSSETT  :  DISTRIBUTION    [Mar.  12th, 

taken  by  the  cable  rather  lower  than  the  result  obtained  by  the  other 
methods,  it  was  found  that  when  the  jute  cables  were  switched  on  less 
current  was  taken  by  the  motor  than  before,  no  doubt  owing  to  the 
efficiency  of  the  alternator  being  improved  by  the  alteration  in  wave- 
form. This  does  not  include  the  increase  of  efficiency  due  to  the 
reduced  exciting  current,  as  the  exciting  current  was  separately 
measured. 

This  objection  could  probably  be  got  over  by  adding  an  inductive 
load  at  the  same  time  as  the  cable,  and  adjusting  it  until  the  wave-form 
of  the  alternator  was  of  equivalent  shape.  This  could  be  proved  by 
either  taking  oscillograph  waves  of  the  potential,  or  preferably  by  con- 
necting up  a  condenser  (another  cable  might  be  used  for  the  purpose) 
and  adjusting  the  inductive  load  until  the  current  flowing  into  the  con- 
denser was  the  same  as  without  the  cable  under  test.  The  inductive 
load  would  be  produced  by  an  air  core  choker,  and  could  be  calculated 
and  deducted  from  the  total  increase  in  power  taken  by  the  motor. 
Owing  to  lack  of  time,  no  definite  results  were  obtained  by  this  method. 
The  motor  alternator  experiments  are  of  value,  however,  in  showing 
the  great  difference  between  the  V.B.  cable  and  the  others. 

The  improvement  in  efficiency,  apart  from  the  reduction  in 
exciting  energy,  caused  by  connecting  circuits  having  capacity  is 
a  factor  to  be  reckoned  with  when  condemning  the  wastefulness  of 
high-pressure  cables. 

TABLE  No.iiV. 

Effect  of  Capacity  on  Exciting  Current. 


Exciting 

Exciting 

Watts  saved 

Approx. 
Watts  in 

VolUgc  on  Cable. 

Current  with- 

Current  with 

in 

out  Cable. 

Cable. 

Excitation. 

Cable  (Paper) 

10,000 

5-8 

25 

426 

2,000 

A 

i     5,000 

5-8 

47 

142 

52^ 

(      2,000 

5-8 

5*4 

52 

80 

r  10,000 

17-5 

13-2 

555 

2,000 

B 

\    5>ooo 

17*5 

i6'o 

193 

500 

i 

(    2,000 

17-5 

172 

39 

80 

A— 30  K.W.  Alternator.        B— 120  K.W.  Alternator. 
Note  : — In  addition,  there  is  a  further  improvement  in  the  efficiency 
of  the  Alternator,  due  to  the  effect  of  the  altered  wave  form  on  the 
armature  losses. 


Table  No.  V.  gives  the  reduction  in  excitation  energy  in  various 
cases,  and  it  will  be  noticed  that  the  saving  is  quite  comparable 
with  the  loss  by  dielectric  hysteresis ;  so  that  beyond  the  objection  to 
running  a  larger  generator  than  is  required  to  supply  the  actual  watts 
consumed,  there  is  really  no  great  loss  due  to  the  use  of  high-tension 
cables,  at  any  rate  at  2,000  volts.     In  the  summary,  however,  dielectric 


1908.]  LOSSES   IN  ELECTRIC  SUPPLY   SYSTEMS.  721 

hysteresis  losses  are  included,  as  exciting  energy  is  not  considered  in 
this  paper. 

The  effect  of  variation  of  voltage  is  shown  in  experiments  No.  15-20. 
It  will  be  seen  that  with  the  particular  form  of  wave  applied  the  current 
increases  rather  more  rapidly  than  the  voltage,  and  the  watts  rather 
more  rapidly  than  the  voltage  squared.  This,  of  course,  means  that 
with  very  high  voltages  the  watts  absorbed  may  be  a  formidable  quan- 
tity ;  but  at  the  same  time  it  must  be  remembered  that  as  the  voltage 
increases,  so  does  the  thickness  of  the  dielectric.  The  capacity  is 
therefore  less,  and,  assuming  no  resonance,  the  cable  volt -amperes  and 
the  watts  absorbed  will  by  no  means  increase  as  the  voltage  squared. 

Some  experiments  were  made  on  the  effect  of  frequency,  and  the 
power-factor  does  not  seem  to  be  largely  altered.  As,  however,  there 
was  some  doubt  as  to  the  accuracy  of  the  instruments  employed  in  these 
tests,  the  figures  are  not  here  recorded. 

The  effect  of  load  on  the  cable  on  this  loss  has  not  been  satisfactorily 
investigated.  It  implies  taking  the  difference  of  two  very  large  quan- 
tities, compared  with  the  loss,  and  is  therefore  not  susceptible  of  much 
accuracy.  In  any  case,  the  time  during  which  the  feeders  in  a  lighting 
station  are  loaded  is  so  small  a  fraction  of  the  whole  time  they  are 
running  that  the  difference  in  the  total  result  cannot  be  large. 

Taking  a  comprehensive  view  of  the  above  results,  there  appears  to 
be  no  doubt  that  in  the  case  of  the  V.B.  insulated  cable.  No.  7,  the 
power-factor  is  of  the  order  of  0*12,  that  of  the  jute-insulated  cables 
about  0*025,  ^^^  of  t^®  paper-insulated  cables  something  of  the  order 
of  0*032  and  o'o8  respectively  for  Nos.  10  and  1 1 ;  the  first  three  results 
are  fairly  consistent  with  all  the  statements  made  in  the  discussion  on 
Mr.  Mordey's  paper.  The  V.B.  cable  appears  to  be  an  exceptionally 
bad  cable  from  this  point  of  view,  and  the  5,000-volt  paper  cables 
appear  to  have  ^  larger  dielectric  hysteresis  loss  than  the  jute 
cables.' 

It  is  noteworthy  that  the  cable  which  shows  an  abnormally  high 
power-factor,  viz..  No.  7,  is  laid  in  an  iron  trough  with  iron  cover. 

It  is  possible  that  this  iron  trough,  completely  surrounding  the  cable, 
accounts  to  some  extent  for  the  high  power-factor. 

Where  the  cable  is  in  an  iron  trough  with  a  tile  cover,  as  in  the  case 
of  Nos.  10  and  11,  the  power-f actor  is  also  higher  than  would  be  ex- 
pected from  the  type  of  cable.  All  the  cables  in  Exp.  12  have  the 
outers  of  slightly  larger  sectional  area  than  the  inners — roughly,  5  per 
cent,  to  10  per  cent,  larger. 

The  fact  that  an  external  field  exists  round  these  cables  is  proved  by 
the  humming  noise  produced  in  the  telephones  connected  to  pilot  wires 

'  The  thickness  of  the  dielectric  between  conductors  of  cables  No.  7, 10, 11, 
and  13  is  0*28  in.  The  thickness  over  the  outer  is  O'lo  in.,  except  for  No.  7, 
in  which  it  is  0*25  in. 

The  iron  trough  in  which  the  cables  are  laid  is  approximately  3J  in.  by 
3j  in.  outside  and  i  in.  thick. 

Cable  No.  4  is  armoured  with  steel  tape,  but  the  thickness  is  only  about  ^  in., 
and  the^outer  and  inner  conductors  are  of  the  same  section. 

The  capacity  of  the  V.B.  insulated  cable  is  abnormally  high,  being  over 
hrce  times  that  of  a  similar  paper  cable. 


722        CONSTABLE  AND   FAWSSETT  :  DISTRIBUTION    [Mar.  12th, 

laid  parallel  and  close  to  the  cables.  That  this  noise  is  not  due  to 
leakage  entirely  is  shown  by  the  fact  that  it  is  slight  during  times  of  no 
load,  and  very  loud  at  times  of  heavy  loads.  Public  telephone  cables 
along  the  same  route,  but  further  away  from  the  lighting  cables,  are 
not  appreciably  affected. 

Taking  the  values  given  above,  the  total  hysteresis  loss  in  the 
Croydon  system  of  mains  comes  out  at  about  17,000  units  per  annum, 
and  is  approximately  equally  divided  between  the  four  quarters.  This 
is  not  so  large  a  loss  that  it  is  worth  while  shutting  down  feeders  for  the 
period  of  light  load  to  reduce  it  considering  the  risks  involved  in  so  doing. 
It  is  most  important,  however,  to  decide  on  a  dielectric  which  will  not 
give  an  abnormal  loss,  as  in  the  case  of  Cable  No.  7. 

Transformer  Losses. 

The  next  point  to  be  considered — and  it  is  one  of  more  importance 
than  losses  in  the  cable  dielectrics — ^is  that  of  transformer  losses  in  an 
alternating  current  supply. 

TABLE  No.  VI. 

Transformer  Losses. 

Maximum  Load  supplied  1,250  k.w. 

Maximum  Tranformer  k.w.  in  use      i»790 

Minimum  Transformer  k.w.  in  use     920 


S! 


Total  losses  during  time  of  heavy  load     88,800  units  per  ann. 
^  ,  Total  losses  during  time  of  light  load...    31,200  do. 

(c)  Total  loss  during  £iy  load        53i200  do. 

Total  losses  per  annum  ...  173,200  units. 

September 
June  Quarter.  and  March  December 

Quarters.  Quarter. 

Note  :  Period  (a)  is  as  follows  (     8  p.m.  to       5  p.m.  to      2.30  p.m.  to 

(12  midnight.  12  midnight.  12  midnight. 

„        (6)  „  (  12  midnight   12  midnight     12  midnight 

(    to  3  a.] 


m.        to  5  a.m.        to  2.30  p.m. 

to        5  a.m.  ' 
8  p.m.  5  p.m. 


(c)  „  (3  a.m.  to        5  a.m.  to 


Table  VI.  gives  the  annual  losses  in  the  transformers  necessary  to 
deal  with  1,250  k.w.  output  at  the  Croydon  station.  These  transformers 
are  placed  in  26  sub-stations  scattered  over  the  district,  and  the  total 
number  of  56  of  1,790  k.w.  total  capacity  is  made  up  of : — 

2  — 100  k.w. 
19  —  50  k.w. 
26  —   20  k.w. 

3—27  k.w. 

6  smaller  sizes. 


903.] 


LOSSES  IN  ELECTRIC  SUPPLY  SYSTEMS. 


723 


These  are  all  in  use  at  times  of  full  load,  and  the  number  does  not 
include  spares.  The  loss  is  cut  down  as  far  as  possible  by  switching  o£E 
transformers  not  required  for  load.  An  attendant  frequently  visits  the 
sub-stations  for  this  purpose. 

Notwithstanding  this  method  of  securing  economical  working,  the 
aggregate  losses  are  very  large. 

If  all  the  transformers  were  kept  on  continually,  the  additional  core 
losses  would  amount  to  40,000  units  at  least  per  annum. 

As  an  attendant  must  in  any  case  visit  the  sub-stations,  the  saving  by 
this  method  of  working  is  very  considerable. 

The  losses  given  in  the  table  are  as  nearly  as  possible  the  average 
losses  in  ordinary  working.  The  core  loss  in  a  particular  100  k.w. 
transformer,  however,  was  979  watts  as  minimum,  with  an  applied 
voltage  wave  as  shown  on  Curve  No.  19,  Sheet  B,  and  1,078  watts  as 
maximum,  with  a  wave  as  shown  on  Curve  No.  8,  Sheet  C. 

As  this  difference  is  so  considerable,  it  was  of  interest  to  investigate 
the  variations  of  wave-form  occurring  in  ordinary  working  throughout 
the  twenty-four  hours.  The  results  obtained  are  most  striking,  and  very 
different  to  what  were  expected. 

The  curves  obtained  serve  to  emphasise  what  is  often  not  fully 
realised,  namely,  that  the  wave-form  obtained  from  any  given  alternator 
is  almost  as  largely  dependent  on  the  kind  of  load  it  is  called  upon  to 
carry  as  upon  the  design  of  the  alternator.  The  curves  were  traced  on  a 
Duddell's  oscillograph,  and  the  main  connections  made  to  obtain  them 
were  as  shown  in  Diagram  No.  VI.,  and  were  such  as  not  to  alter  the 
normal  running  conditions  to  any  appreciable  extent. 


Diagram  No   VI. 


LB  is  the  live  bus-bar  and  EB  the  earthed  bar,  the  system  of  supply 
being  2,000  volts  with  one  pole  earthed.  Di,  D2,  D3  are  the  alternators  ; 
Fi,  F2,  F3  are  the  feeders ;  Ri  is  a  non-inductive  shunt  carrying  the 
whole  current,  and  R3  and  R4  are  non-inductive  resistances  used  as  a 
potential  divider  to  reduce  the  voltage  from  2,000  across  the  bus-bars 
to  the  necessary  2  volts  on  the  oscillograph  ;  it  consisted  of  a  bank  of 


} 


724        CONSTABLE  AND   FAWSSETT:  DISTRIBUTION     [Mar.  12th, 

lamps  with  a  small  non-inductive  resistance,  R4  in  series  with  it,  across 
which  the  oscillograph  voltage  strip  was  connected  ;  Ri  consisted  of 
brass  condenser  tubes  arranged  non -inductively,  and  tested  for  absence 
of  self-induction.  The  height  of  the  current  waves  was  adjusted  by 
altering  the  value  of  the  shunt,  and  also  by  means  of  an  adjustable 
resistance  R2,  in  series  with  the  oscillograph  current  coil. 

The  curves  are  sensibly  correct  in  shape,  but  there  may  be  slight 
errors  due  to  their  having  been  twice  traced.  There  is  also  noticeable 
a  slight  difference  in  the  horizontal  width  of  the  two  half  periods,  due, 
no  doubt,  to  a  slight  want  of  uniformity  in  the  rotation  of  the  mirror  of 
the  instrument.    This  error  can,  however,  be  allowed  for. 


\G 


TABLE  No.  VII. 
Variation  of  Wave  Form  during  24  Hours. 


R.M.S.  Values. 

No.  of 

Curve, 

Sheet  A. 

Time. 

Machines 
Running. 

Remarks. 

Bus-bar 

Total 

Volts. 

amperes 

P.M. 

I 

3.40 

2,090 

58 

5 

Transformers  all  on. 

3 

4.10 

2,090 

90 

5»7 

3 

4.15 

2,090 

1 10 

5,7 

4 

4-30 

2,090 

210 

4,5»7 

5 

445 

2,100 

350 

i>4i5>7 

Some  arcs  on. 

6 

5.5 

2,100 

505 

h  2,  4i  5i  7 

( All  arcs  on  (150  amps. 
(     for  arcs.) 

I 

540 

2,110 

534 
558 

1,2,3,4,5,7 

6.50 

2,110 

1,2,3,4,5,7 

Maximum  load. 

9 

9-5 

2,100 

340 

4,5,7 

10 

9.15 

2,100 

310 

5,7 

Some  transformers  oflF. 

II 

1 1.5 

2,100 

215 

5,7 

12 

"•35 

A.M. 

2,100 

170 

7 

13 

12.30 

2,080 

124 
118 

3,4 

H.N.  arcs  off. 

(  I  Transformer  in  each 

(     Substation  on  only. 

14 

2.10 

2,070 

3,4 

15 

4.50 

2,070 

103 

3,4 

16 

6.3 

2,070 

114 

3,4 

]l 

2-^5 

2,070 

130 

3,4 

Some  A.N.  arcs.  off. 

2-^ 

2,070 

63 

3,4 

All  arcs  off. 

19 

8.25 

2,070 

43 

2 

20 

8.45 

2,070 

32 

2 

v> 


N.B. — ^The  P.D.  waves  are  all  to  the  same  scale,  but  the  current 
waves  are  to  different  scales. 


Sheet  A  gives  the  curves  obtained  on  January  20th,  1902,  and  Table 
VII.  is  the  key  to  the  reference  numbers.  Sheet  B  gives  the  curves 
obtained  on  July  26th  of  the  same  year,  and  Table  VIII.  is  the  corre- 
sponding key.  Sheet  C  gives  the  voltage  wave-forms  of  the  various 
alternators  'running  light,  and  also  some  miscellaneous  waves,  and 


SG  TWENTY-FOUR   HOURS. 

P.O Current 

5 


dK, 


1903.]  LOSSES  IN  ELECTRIC  SUPPLY  SYSTEMS. 

TABLE  No.  VI  IT. 
Variation  of  Wave  Form  during  24  Hours. 


726 


No.  of 
Curve, 

Time. 

Bus-bar 

Total 

Machines 
Running. 

Remarlcs. 

Sheet  a 

VoIU. 

Amps. 

6.50 

(  All  transformers  on. 
(  5,000  volt  cable  on  load. 

I 

2,070 

32 

7 

2 

7.25 

2,075 

70 

7 

3 

7.50 

2,080 

140 

6,7 

4 

8.12 

2,100 

260 

5,6,7 

All  arcs  on. 

5 

8.58 

2,115 

510 

5,6,7 

Maximum  load. 

6 

10.50 

2,100 

310 

5,7 

I 

11.30 

2,100 

200 

7 

I 

12  mdnt 

2,090 

IIO 

7 

^H.N.  arcs  off. 

9 

12.15 

2,090 

1 10 

4,7 

10 

I  a.m. 

2,090 

100 

4 

Only  a  few  transformers  on. 

II 

2.55 

2,060 

85 

4 

12 

3-32 

2,060 

30 

4 

Some  arcs  off. 

13 

4-5 

2,050 
2,060 

26 

3 

All  arcs  off. 

14 

7-5 

18 

3 

5,000  volt  cable  off. 

15 

7.10 

2.060 

26 

3 

„        „        „    on. 

iS 

10.50 

2,060 

26 

1,3 

„        „        „     „ 

17 

11.20 

2,060 

26 

I 

„        „        „     „ 

18 

2,060 

(  5,000  volt  cable  on  and 

415 

24 

I 

)      Rect.  Arcs  Circuit. 

*i9 

640 

2,060 

30 

I 

1 5,000  volt  cable  and  all 
(     transformers  on. 

20 

7.30 

2,060 

30 

7 

„        „        1,        ,1 

*  This  current  ciure  was  actually  taken  before  No.  i,  and  the  volt 
curve  interpolated  from  previous  records. 

N.B. — ^The  D.P.  waves  are  all  to  the  same  scale,  but  the  current 
waves  are  to  different  scales. 


Table  IX.  is  the  key  to  this  sheet.  The  sine  waves  equivalent  to  the 
various  voltage  waves  are  shown  by  dotted  lines.  The  normal  periodi- 
city is  60  per  second. 

The  curves  have  not  been  taken  at  regular  intervals  of  time,  but  only 
when,  owing  to  some  alteration  in  the  kind  or  magnitude  of  the  load, 
there  was  likely  to  be  a  change  in  the  shapes  of  the  waves. 

The  alternators  are  all  of  the  iron  core,  slot  wound,  revolving  arma- 
ture type,  with  large  percentage  regulation.  Nos.  i,  to  5  were  designed 
to  be  short-circuited  with  impunity.  They  are  direct-coupled  to  their 
engines  and,  under  normal  conditions,  run  perfectly  in  parallel  at  all 
loads. 

On  comparing  the  two  sheets  A  and  B,  the  first  noticeable  point  is 
the  remarkably  peaked  waves  in  B.  The  only  difference  was  the 
addition  of  a  feeder  working  at  5,000  volts  and  3-6  miles  long,  a  few 
other  2,000- volt  and  200- volt  cable  extensions,  and  also  No.  6  alternator. 

The  effect  of  this  increased  capacity  is  to  totally  alter  the  shape  of 
the  current  waves  and  to  appreciably  alter  the  voltage  waves. 


726        CONSTABLE  AND  FAWSSETT :  DISTRIBUTION     [Mar.  12th, 
TABLE    No.    IX. 


3^ 

Alter- 

Description of  Curve 

nator 

R.M.S.  VoUs. 

No. 
M.A. 

1 

'  I  P.D.  Curve  30  k.w.  Motor-driven  Alternator 
1                                   running  light 

2,060 

2        M        ),    120  k.w.  Alternator  running  light 

I 

t» 

3  1      »»         »»      »f      »i            i>                >»            >» 

3 

M 

4     1          »»                »»          »f          M                       f»                              »l                       M 

3 

„ 

5  '     »»         »»    25^   »            f»               »f           >» 

4 

6    '          »»                •!           »»          >»                       f»                              »•                       M 

5 

»f 

7 

»»                 .»       500      ».                       If                              M                       »t 

6 

» 

0 

(P.D.    Curves   of    Rectifier,    Applied    and) 

7 

'  Applied :  2,080 
(Rectified:  168 

9 

Rectified  volts,  Rectifier  running  on  small  \ 
Transformer  loaded                                    J 

... 

10 

P.  D.  Curve  500  k.w.  Alternator  running  light 

6 

2,090 

II 

»»         »»       »»      »»            »»               »»          »» 

7 

t» 

„         „     Nos.   6   and   7    Alternators   in) 

2,090 

12 

parallel ;    synchronising  cur-  ■ 

... 

Current  about 

rent  curve  dotted 

15  amps. 

(  V         i»     30  k.w.  Alternator  running  light ) 

1                        at    15-3  r\J ,   on    5,000   volt  I 

... 

13 

1                        cable    through    200  volts  —  " 
V                       2,000  volt  transformer 
P.D.  Curve  of  30  k.w.  Alternator  loaded  to 

2,045 

14 

16  k.w.  running  at  60  rvj  ,  on  5,000  volt  . 
cable  alone                                                 ) 

... 

2,050 

15 

Current  Curve,  30  k.w.  Alternator  light  at 
30  r>j  ,  on  5,000  volt  cable 

... 

Current:  0*58  amp. 

P.D.  Curves  of  Primary  and   Secondary) 

(  Primary  :  2,100 
I  Secondary:  5,250 

16 

volts    on    2,000  —  5,000   volt    100   k.w.  I 
transformer                                                J 

... 

Note  :— All  the  Alternators  have  slotted  iron  cores,  revolving  armatures 
and  laminated  poles. 


It  is  interesting  to  notice  how,  with  the  load  consisting  chiefly  of 
cables,  the  current  is  leading.  As  the  load  increases,  the  current  and 
voltage  Waves  approach  each  other  in  phase  and  the  irregularities  are 
smoothed  out.  Late  at  night  when  the  load  is  mostly  arc-lighting,  the 
current  lags.  Some  very  remarkable  effects  are  produced  by  the  flat- 
topped  wave  of  No.  7  alternator,  as  shown  in  Curve  No,  12,  Sheet  A, 
and  Curve  Nos.  7,  8  and  9,  Sheet  B. 

On  Sheet  C  the  additional  curves  are  exceptional,  and  show  what 
remarkable  effects  may  be  produced  by  suitable  combinations  of  capa- 
city and  inductance.  These  were  obtained  with  the  ordinary  plant  of 
the  station  in  the  course  of  some  miscellaneous  experiments,  and  they 
point  out  the  necessity  of  not  allowing  abnormal  conditions  to  ariSe  in 
working,  or  the  safety  of  the  cables  and  transformers  may  be  seriously 


VARIATION  OF  VOLTAGE  AND  CU 


She 


1903.]  LOSSES  IN  ELECTRIC  SUPPLY  SYSTEMS. 


727 


VOLTAGE  WAVE   FORMS  OF  ALTERNATORS,   ETC. 


^, 


Vol.  82. 


3HPET  G  (SEK  Table  No.  IX.). 
48 


728        CONSTABLE   AND   FAWSSETT:   DISTRIBUTION     [Mar.  12th, 

endangered.  Curves  Nos.  lo,  ii,  and  12  on  this  sheet  show  respectively 
the  voltage  curves  of  alternators  Nos.  6  and  7  running  singly  and  also  in 
parallel.  The  dotted  curve  in  No.  12  represents  the  synchronising 
current  flowing  between  the  two  machines,  its  R.M.S.  value  being 
about  15  amperes.  The  voltage  curve  of  the  two  in  parallel  is  prac- 
tically the  mean  of  the  separate  curves.  In  connection  with  the 
general  question  of  parallel  running  of  alternators,  the  following  result 
is  interesting  :  On  one  occasion  an  attempt  was  made,  for  convenience 
in  practical  working,  to  join  up  two  machines  in  parallel  through  two 
concentric  cables,  each  about  four  miles  long.  Under  these  conditions 
the  machines  would  not  keep  in  phase  at  all,  although  under  normal 
conditions  they  ran  perfectly  together. 

Meter  Losses. 

The  question  of  meter  losses  now  remains  to  be  dealt  with. 

There  are  in  use  in  the  district  being  considered  rather  more  than 
1,200  meters,  and  the  same  number  of  Wright's  Demand  Indicators. 
About  1,000  of  these  meters  are  Thomson  meters,  and  the  rest  of  the 
Westinghouse  Co's  manufacture. 

The  shunt  losses  are  by  far  the  most  serious,  as  these  go  on  con- 
tinuously, and  they  amount  to  a  total  of  37,400  units  per  annum. 

As  is  well  known,  the  shunt  loss  of  a  Thomson  meter  is  rather  high ; 
the  Westinghouse  meter,  however,  only  takes  about  i  watt  in  the 
shunt. 

The  series  coil  losses,  worked  out  from  the  load  curves  for  private 
lighting,  only  reach  a  total  of  1,350  units  per  annum  for  both  meters 
and  demand  indicators.  This  low  figure  is  due  to  the  short  hours  the 
meters  have  any  appreciable  load  on  them,  and  to  the  fact  that  in  the 
majority  of  cases  the  meter  is  never  run  at  its  rated  full  load. 

In  fact,  the  total  amperage  of  meters  installed  is  about  3*6  times  the 
maximum  current  used  for  private  lighting. 

It  is  evident  that  a  large  economy  could  be  effected  by  abolishing 
the  shunts  altogether  and  using  ampere-hour  meters.  The  only  difficulty 
is  the  variation  of  the  consumers'  pressure  from  the  supply  standard. 

In  very  few  cases,  however,  is  the  variation  more  than  the  limit  of 
inaccuracy  allowed  in  the  meters,  and  on  the  average  the  standard  pres- 
sure will  be  very  nearly  kept  to. 

Using  an  energy  meter,  the  consumer  who  gets  a  good  pressure 
pays  a  little  more  for  his  ampere-hours  than  he  otherwise  would,  and  is 
well  satisfied.  In  the  case  of  an  ampere-hour  meter,  the  consumer  with 
a  bad  pressure  pays  for  rather  more  units  than  he  uses,  but  he  will  not 
notice  the  difference  in  his  bill,  and  he  will  complain  of  the  bad  light 
in  any  case. 

There  are  further  advantages  in  using  ampere-hour  meters,  viz., 
cheapness,  ease  of  installing  and  less  risk  of  breakdown. 

The  large  loss  in  the  shunts  given  above  is  due,  of  course,  to  the 
particular  type  of  meter  in  use,  but  the  Thomson  meter  is  not  the  worst 
in  this  respect,  though  it  is  far  from  being  the  best. 

So  far,  the  losses  have  been  enumerated  without  much  reference  to 


1903] 


LOSSES   IN   ELECTRIC   SUPPLY  SYSTEMS, 


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19W.]  LOSSES   IN   ELECTRIC   SUPPLY   SYSTEMS.  731 

the  total  output  of  the  station.  In  Table  No.  X.  the  whole  of  the  losses 
are  summarised  and  expressed  as  percentages  of  the  total  units  gener- 
ated and  the  total  units  sold. 

Diagram  No.  VII.  is  a  graphic  representation  of  the  losses  as  they 
occur  in  the  system. 

It  will  be  seen  from  the  Table  that  the  calculated  loss  is  22  per  cent, 
of  the  units  sent  out  of  the  station.  From  the  actual  sum  of  the  con- 
sumers' meter  readings,  however,  the  loss  appears  to  be  only  18*4  per 
cent.  This  difference  of  3*6  per  cent,  is  no  doubt  partly  due  to  a 
rather  liberal  estimate  of  the  losses  in  some  cases  :  numerous  approxi- 
mations are  required,  and  it  is  impossible  to  calculate  the  losses  with 
great  accuracy.  It  may  also  be  partly  due  to  small  errors  in  the  meters. 
The  total  units  generated  depend  on  the  average  accuracy  of  seven 
meters,  whilst  the  total  sold  depends  on  1,200— a  difference  of  2  or 
3  per  cent,  may  thus  easily  occur. 

There  is  a  further  side  to  the  question  which,  however,  as  it  hardly 
comes  within  the  scope  of  this  paper,  will  be  briefly  dealt  with.  It 
may  be  economical  to  waste  energy  as  long  as  interest  has  to  be  paid  on 
borrowed  money.  It  is,  of  course,  possible  to  reduce  C'R  losses  at  any 
rate  to  a  negligible  amount,  by  putting  in  enough  copper,  but  it  is  not 
economical  to  do  so. 

It  is  the  duty  of  the  engineer  to  design  a  system  which  shall  give 
the  best  result  for  the  least  annual  expenditure ;  he  must  avoid  losses 
in  transmission  up  to  the  point  where  the  expense  of  avoiding  them 
becomes  greater  than  the  cost  of  the  energy  lost.  A  case  illustrating 
the  comparative  advantages  of  two  alternative  schemes  is  the 
following : — 

A  certain  portion  of  the  district  considered  in  this  paper  was  origin- 
ally supplied  with  alternating  current  from  four  sub-stations,  fed  at 
2,000  volts.  After  a  few  years  the  load  became  much  heavier  than  at 
first,  and  it  was  found  both  more  economical  and  advisable  for  other 
reasons  to  change  the  supply  to  direct  current  without  transformation, 
using  the  sam«  low-tension  mains,  instead  of  adding  to  the  section 
of  the  existing  cables.  The  total  losses  per  annum  under  the  old 
system  amounted  to  49,100  units.  With  the  new  system  for  the  same 
load  the  losses  are  40,300  per  annum,  so  that  there  is  a  saving  of  8,800 
units  in  favour  of  the  direct-current  supply,  and  the  cost  of  the  altera- 
tion was  considerably  less  than  that  of  the  other  alternative. 

The  average  distance  of  these  sub-stations  from  the  generating 
station  is  1,290  yards,  or  about  three-quarters  of  a  mile,  and  the  maxi- 
mum load  is  about  400  k.w.  in  all. 

With  regard  to  the  means  for  reducing  the  losses  in  general  to  a 
minimum,  the  methods  to  be  adopted  have  been  mentioned  under  the 
various  sections  of  this  paper,  but  they  may  be  summarised  here. 
Primarily  good  design  is  necessary  ;  after  that,  care  must  be  taken  to 
remove  useless  causes  of  waste  during  times  of  light  load. 

The  cure  for  waste  of  energy  in  switchboards  and  station  connec- 
tions is  simple  design,  good  workmanship,  and  choice  of  suitable  posi- 
tions. Cable  losses  may  be  reduced,  assuming  suitable  dielectrics  have 
been  selected,  by  switching  off  high-tension  cables   not   required  for 


732        CONSTABLE  AND   FAWSSETT  ;  DISTRIBUTION     [Mar.  12th, 

load,  but,  as  in  most  cases  the  saving  by  doing  this  is  small,  the  extra 
risk  of  cable  breakdowns  more  than  counterbalances  it. 

C»R  losses  in  the  low-tension  system  may  be  cut  down  by  inter- 
connecting the  network  so  as  to  use  all  the  copper  laid  down,  to  the 
best  advantage.  Fuses  between  the  various  sections  must  be  relied  on 
in  case  of  breakdown  if  this  is  done. 

Transformer  losses  during  light  loads  are,  of  course,  reduced  by 
switching  out  transformers  which  are  not  necessary.  This  practice  is 
not,  in  the  opinion  of  the  authors,  detrimental  to  the  safety  of  a  well- 
made  transformer.  It  may  certainly  pay  in  some  cases  to  scrap  trans- 
formers of  an  old  and  wasteful  type,  rather  than  to  use  them  until  they 
are  worn  out.  It  may  be  worth  while  to  either  artificially  alter  the 
wave  shape  during  the  day,  or  to  run  machines  with  a  peaked  wave  in 
order  to  reduce  the  core  loss. 

It  is  hardly  admissible  to  alter  the  frequency  unless  no  motors  what- 
ever are  in  use. 

To  remove  the  largest  source  of  loss  in  meters,  shunts  should  be 
abolished,  as  discussed  in  the  section  on  meters. 

Although  this  paper  deals  with  the  Croydon  system  of  distribution, 
the  arguments  hold  good  generally,  whether  the  supply  is  by  means  of 
alternating  or  direct  current. 

The  question  of  losses  in  tramways  or  power  schemes  is  consider- 
ably modified,  however,  by  the  altered  conditions  of  working. 

There  are  in  such  cases  only  a  few  hours  of  light  load  instead  of  the 
larger  part  of  the  day,  and  as  the  losses  will  be  practically  all  C"R  loss 
in  the  cables,  much  heavier  copper  must  be  put  in  to  secure  the  most 
economical  working. 

The  losses  detailed  in  this  paper  are  incurred  in  a  system  which  is 
indisputably,  on  the  whole,  well  arranged  and  economically  worked. 
The  district  has  the  disadvantage  of  being  a  very  extended  one,  so  that 
the  number  of  consumers  per  mile  of  mains  is  small.  This  accounts  for 
part  of  the  large  C"R  losses,  but  even  so  the  remainder  is  of  very  con- 
siderable magnitude,  and  there  must  be  many  supply  systems  working 
under  worse  conditions. 

The  engineers  of  these  systems  will,  however,  probably  feel  hurt  if 
they  are  told  that  they  are  guilty  of  slowly,  but  surely,  throwing  away 
the  coal  resources  of  the  Empire,  and  that  they  are,  therefore,  neither 
serving  their  profession  or  their  country  in  the  highest  degree. 

In  conclusion,  the  authors  wish  to  heartily  thank  Mr.  Minshall  for 
his  help  and  many  suggestions,  and  also  to  thank  his  successors  at 
Croydon  for  their  kind  permission  to  complete  the  necessary  experi- 
ments and  to  publish  these  results.  Several  members  of  their  staff 
have  also  merited  thanks  for  much  valuable  assistance  and  unflagging 
interest  in  the  experimental  work.  A  tribute  is  due  to  Mr.  Duddell  for 
having  placed  on  the  market  so  beautiful  an  instrument  as  his  oscillo- 
graph ;  but  for  the  interest  attached  to  the  use  of  this  instrument,  this 
paper  would  not  have  been  written. 


1908.]              LOSSES   IN   ELECTRIC  SUPPLY  SYSTEMS.  733 

INDEX  TO  TABLES. 

Description.  Table 

No. 

Losses  in  Switchboards  and  Connections I. 

CR  Losses  in  Cables II. 

Wattmeter  Constants III. 

Results  of  Cable  Tests            IV. 

„       Tests  on  Cables  at  various  points         IVa. 

Reduction  of  Exciting  Energy  due  to  Cables       V. 

Transformer  Losses VI. 

Key  to  Curves,  Sheet  A          VII. 

ft           »           f>      ^          •••        •••         •••        •••         •••        •••  Vlll. 

„          „           ff      C          ...        ...        ...        ...         ...         ...  IX. 

Summary  of  Losses      X. 


INDEX  TO  DIAGRAMS. 

Description.  Diagram 

No. 

Load  Curves  for  Lighting  Station «  I. 

Lighting  Curve  for  Public  Lamps II. 

Connection  for  Wattmeter  Calibration       III. 

„           „    Cable  Tests IV. 

„           „   Motor  Alternator  Tests       V. 

„           „  Station  Wave  Forms           VI. 

Graphical  Analysis  of  Losses            VII. 

Variations  of  Bus-bar  Voltage  and  Main  Current  Waves  Sheet  A. 

ft  tt  ft  ft  »        "' 

P.D.  Waves  of  Alternators  and  Miscellaneous  Wave  Forms         „     C. 


INDEX  TO  CURVES. 

Description. 

Curve 
Current,  Voltage,  and  Watts,  Wave  Forms,  Cable  No.  7         ...        A. 

„  „  „  „  ...  ...  £>. 

tf  ft  tt  tt      No.  9 C. 

„  „  „  Ironless  Choker  ...        D. 

Current  and  Voltage  Wave  Forms,  Cable  No.  11  at  Different 

Voltages E,  F,  &  G. 

Sine  Waves  equivalent  to  Curve  E.  '  H. 

Current  and  Voltage  Wave  Forms,  Cable  No.  1 1  at  Different 

Voltages I,  J,  &  K. 

Current,  Voltage,  and  Watts,   Wave   Forms,  in  Experiment 

No.  12,  Table  IV L. 


734  CONSTABLE  AND   FAWSSETT :  [March  12th, 

Mr.  M.  B.  Field  then  read  an  abstract  of  his  paper,  entitled  "A 
Study  of  the  Phenomenon  of  Resonance  in  Electric  Circuits  by  the 
Aid  of  Oscillograms "  (see  abovef  page  647),  read  before  the  Glasgow 
Local  Section.  ' 

President  The  PRESIDENT :   I  will  not  occupy  the  time  of  the  Institution  in 

complimenting  the  authors  of  these  papers ;  e\'erybody  who  has  looked 
at  them  knows  how  much  we  are  indebted  to  them  for  their  labours. 

^^'Af°^^^  Mr.  Leonard  Andrews  :  Whilst  I  have  been  very  interested  in 
both  the  papers  we  have  listened  to,  I  have  only  a  few  remarks  to 
make  on  the  first  one.  This  question  of  distribution-losses  has  been 
troubling  us  at  Hastings  for  some  years.  Until  two  years  ago 
our  losses  in  the  summer  months  amounted  to  about  50  per  cent, 
of  the  units  generated.  Various  alterations  were  made  to  reduce 
these  losses,  and  last  year,  during  the  months  of  June  and  July, 
they  only  averaged  27*3  per  cent,  of  the  units  generated.  To  roughly 
locate  these  remaining  losses  we  fixed  meters  in  the  sub-stations 
between  the  low-tension  transformer 'bus-bars  and  the  distributing 'bus- 
bars. By  this  means  we  were  able  to  compare  the  units  generated,  the 
units  turned  out  from  the  sub-stations,  and  the  units  metered  to  con- 
sumers. The  losses  in  the  high-tension  feeders  and  transformers  during 
the  two  months  referred  to  amounted  to  16*8  per  cent,  of  the  units 
generated,  and  the  losses  in  the  low-tension  mains  and  consumers'  meters 
to  io*5  per  cent.,  thus  making  the  total  distribution-losses  27*3  per  cent, 
of  the  units  generated.  It  appears  from  Table  10  of  the  authors'  pap>er 
that  the  corresponding  losses  at  Croydon  amounted  respectively  to 
20*8  per  cent.,  9*8  per  cent.,  and  30*8  per  cent,  of  the  units  generated 
durmg  the  summer  months.  At  Hastings  the  whole  of  the  high-tension 
feeders  and  transformers  are  cut  ofif  shorly  after  11  p.m.,  and  are  left 
disconnected  until  sunset  the  following  day.  During  the  hours  of  light 
load  the  supply  is  maintained  through  the  low-tension  network  alone, 
from  one  sub-station  adjoining  the  works.  On  page  16  of  their  paper 
the  authors  suggest  that  the  dielectric  hysteresis  losses  are  insu£Ecient 
to  make  it  worth  while  to  cut  off  the  high-tension  feeders  during  the 
hours  of  light  load,  when  the  risks  involved  in  doing  so  are  considered. 
They  recommend,  however,  that  some  of  the  transformers  should  be 
switched  off  to  reduce  the  transformer-losses.  They  appear  to  have 
overlooked  the  fact  that  the  risk  incurred  in  switching  transformers  on 
and  off  is  probably  quite  as  great  as  switching  feeders  on  and  o£F, 
added  to  which  it  is  a  risk  which  cannot  be  so  easily  dealt  with.  If  the 
feeders  and  transformers  are  switched  off  simultaneously,  as  is  done  at 
Hastings,  some  simple  cable-charging  device  can  be  used  for  this 
purpose,  and  thus  the  rise  of  pressure  in  both  feeders  and  transformers 
can  be  prevented.  That  rises  of  pressure  do  often  occur  when  a  trans- 
forijier  is  excited,  either  from  the  low-tension  or  high-tension  side, 
may  be  seen  by  the  aid  of  an  oscillograph  or  by  connecting  a  spark 
gap  across  the  primary  terminals.  If  the  spark-gap  is  adjusted  to  just 
not  break  down  at  double  the  normal  working  pressure  of  the  primary 
of  the  transformers,  a  spark  will  jump  across  the  gap  at  the  moment 
of  connecting  the  secondary  windings  to  a  low-tension  source  at  normal 


1903.]  DISTRIBUTION   LOSSES  :    DISCUSSION.  736 

pressure.  Quite  apart  from  the  reduction  of  dielectric  hysteresis  Mr.Leonani 
losses  effected  by  switching  off  feeders  during  the  hours  of  light  A"****^^ 
load,  there  is  a  great  advantage  in  tmving  the  whole  of  the  high-tension 
system  dead  in  the  daytime  for  alterations  or  testing.  The  variation  in 
the  shape  of  the  curves  that  the  authors  have  shown  is  very  interesting. 
We  have  also  noticed  that  we  get  a  very  different  shaped  curve  on 
light  load  to  what  we  get  on  full  load,  though  this  difference  only 
appears  to  be  noticeable  on  iron-cored  machines.  The  authors  refer 
to  the  fact  that  they  have  found  that,  imder  certain  conditions,  the 
current  curve  lags  behind  the  E.M.F.  curve.  I  have  been  rather 
surprised  to  notice  that  at  Hastings  under  no  conditions  do  we  get 
a  lagging  current.  Even  when  the  load  is  made  up  of  50  per  cent. 
of  arc  lamps  and  magnetising  current  the  current  still  appears  to  lead. 
This  is  probably  due  to  the  fact  that  there  are  several  miles  of  vul- 
canised rubber  cable  connected  to  the  system.  The  authors  suggest 
that  meter  losses  might  be  reduced  by  doing  away  with  the  shunt- 
windings  in  meters.  I  think  it  would  be  found  that  to  do  this  would 
tend  to  introduce  another,  and  a  much  more  serious,  source  of  loss, 
namely,  that  due  to  the  meters  failing  to  start  on  light  load.  With 
very  small  meters,  that  are  only  expected  to  carry  a  maximum  load 
of  two  or  three  amperes,  this  difficulty  does  not  exist,  and  it  is  probable 
that  with  these  meters  the  saving  effected  by  doing  away  with  the 
shunt-windings  would  more  than  counterbalance  any  loss  due  to  con- 
sumers being  supplied  at  a  pressure  two  or  three  per  cent  above  the 
declared  pressure.  Larger  meters  can,  however,  only  be  relied  upon  to 
start  on  light  loads  if  they  are  constructed  with  shunt-windings.  We 
effected  a  very  considerable  saving  a  few  years  ago  by  taking  out  the 
whole  of  our  ampere-hour  meters  and  replacing  them  by  watt-meters, 
in  spite  of  the  losses  introduced  due  to  the  shunt-windings  of  the  latter. 

Major  P.  Cardew  :  I  will  not  detain  you  very  long,  because.  Major 
although  I  made  three  attempts  during  the  last  week  to  read  these 
very  interesting  papers,  they  were  always  stolen  from  me,  and  I  have 
not  been  able  to  get  through  them.  The  point  that  forcibly  occurs 
to  me,  looking  back  to  the  time  when  we  were  settling  regulations, 
is  how  lucky  it  was  that  we  stipulated  that  all  cables  were  to  be  tested 
with  twice  the  working  pressure  with  one  hour,  seeing  what  a  tre- 
mendous amount  of  increase  of  pressure  you  get  from  these  exag- 
gerated ripples.  If  that  is  carried  out,  I  think  the  cables  ought  to 
stand  all  that  they  are  likely  to  be  subjected  to,  even  from  the  amount 
of  resonance  that  may  take  place.  There  is  no  doubt  that  the  charging 
of  a  cable  is,  in  all  respects,  very  much  like  dealing  with  a  live  load 
on  a  bridge.  I  think  a  practical  way  to  look  at  it  is  that  the  cable 
most  be  strong  enough  to  stand  the  extra  stress  which  comes  upon  it. 
At  the  same  time,  it  occurs  to  me  that,  with  a  view  to  diminishing 
to  some  extent  the  danger  to  cables  on  systems  with  high  pressures, 
something  might  be  done  in  modifying  the  switching  arrangements 
—the  switching  on  and  off.  As  far  as  I  have  read  the  discussion 
on  this  paper,  and  on  all  other  papers,  it  is  always  taken  that  the 
al>solute  charge — the  contact — is  an  instantaneous  thing ;  but  when 
we  see  what  a  lot  may  happen  during  one  period  of  a  fiftieth  of  a 


736 


ELECTIONS. 


[Mar.  ISth, 


Major 
Cardew. 


second  it  occurs  to  me  that  the  absolute  contact  is  not  by  any  means 
instantaneous,  and  that  the  cable  is  really  eased  up  at  high  pressures- 
pressures  of  5,000  volts  and  upwards — by  the  arc  which  takes  place  as 
the  switch  is  closed.  And,  more  than  that,  we  must  consider  the  efiFect 
of  the  closing  switch  as  being  to  some  extent  an  adjustable  condenser, 
rapidly  increasing  its  capacity  and  in  series  with  the  capacity  of  the 
cable.  That  being  so,  of  course  the  voltage  condensed  on  the  moving 
contacts  of  the  switch  is  continually  diminishing  as  the  charge 
increases ;  and,  on  the  other  hand,  the  voltage  condensed  across 
the  cable  is  gradually  increasing  all  that  time.  By  some  arrangement 
which  will  give  more  capacity  effect  to  the  switch  as  it  closes,  I  think 
very  considerable  relief  could  be  obtained. 

The  President  announced  that  the  scrutineers  reported  the  fol- 
lowing candidates  to  have  been  duly  elected  : — 

Members, 
Daniel  Coyle.  |      Joseph  Wilkinson. 

Associate  Members. 


Rooke  Ainsworth. 
Ekiward  Calvert. 
Samuel  McLean. 
Charles  Andrew  Newton. 


John  Walter  Parr. 
Charles  Norman  Robinson. 
Walter  Stewart. 
George  Gordon  Tomkins. 


Associates. 


Arthur  Baker. 

James  Stephen  Blackwell. 

Joseph  Boyce. 


Thomas  William  Storey. 


William  John  Charlton. 
Thomas  Dow  Frew. 
John  Jamieson. 


Students. 


Charles  Reed  Allensby. 
William  George  Herbert  Cam. 
Albert  W.  Deakin. 
William  Rowland  Ding. 
Thomas  Ellis. 
Reginald  Woolton  Fowler. 
P.  L.  R.  Fraser. 
James  Frederick  Gay. 
Alexander  Lindsay  Glegg. 
Masanoske  Hayashi. 


Kenneth  Horton. 
William  Howes. 
Clarence  Hambly  Hughes. 
Alfred  James  Munday. 
Thomas  George  Partridge, 
John  G.  Potts. 
Morgan  Howell  Rees. 
Alfred  Ernest  Scott. 
Frederick  Smith. 
Richard  Edward  Wellard. 


1903.]  TRANSFERS.  787 


The  Three  Hundred  and  Ninety-first  Ordinary  General 
Meeting  of  the  Institution  was  held  at  the  Institution 
of  Civil  Engineers,  Great  George  Street,  Westminster, 
on  Thursday  evening,  March  26,  1903 — Mr.  jAMES 
Sv^iNBURNE,  President,  in  the  Chair. 

The  minutes  of  the  Ordinary  General  Meeting  held  on  March  12th 
were  taken  as  read  and  signed  by  the  President. 

The  names  of  new  candidates  for  election  into  the  Institution  were 
taken  as  read,  and  it  was  ordered  that  these  names  should  be  suspended 
in  the  Library. 

The  following  list  of  transfers  was  published  as  having  been 
approved  by  the  Council : — 

From  the  class  of  Associate  Members  to  that  of  Members — 

Reginald  Page  Wilson. 
From  the  class  of  Associates  to  that  of  Members — 

Stephen  Stewart  Goodman. 

From  the  class  of  Associates  to  that  of  Associate  Members — 

Leonard  Breach.  I      Arthur  Frederick  Malyon  Gatrill. 

Edward  Macgregor  Duncan.        |      Thomas  McGill. 
Herbert  James  Read. 

From  the  class  of  Students  to  that  of  Associates- 
Percy  Meares  Crampton. 
Robert  Saunders  Newton. 
Richard  Lloyd  Pearson. 

Messrs.  F.  Graham  and  A.  G.  Inrig  were  appointed  scrutineers  of 
the  ballot  for  the  election  of  new  members. 

The  President  ;  The  Students  have  been  working  very  hard,  and 
have  got  up  a  large  subscription  in  aid  of  the  Building  Fund.  They 
have  collected  no  less  than  £83  6s.,  and  after  deducting  the  various 
small  expenses,  there  is  a  balance  of  £79  los.  6d.  to  add  to  the  Building 
Fund.     I  am  sure  the  Institution  would  like  me  to  read  this  letter  : — 

"  March  26,  1903, 
"  Dear  Mr.  McMillan, — I  enclose  the  balance  sheet  (which  is  a  copy 
of  my  own)  of  our  Students'  Subscription  List  to  The  Building  Fund  of 
the  Institution  of  Electrical  Engineers.  This  fund  was  opened  on 
January  ist  and  closed  on  March  30th  last,  and  through  our  efforts  we 
have  been  able  to  collect,  as  you  will  see,  a  net  amount  of  £yg  los,  6d. 
By  a  motion  of  the  Committee,  I  am  not  to  give  you  a  list  showing  the 
amount  subscribed  by  each  student,  but  just  a  list  of  the  names  of  those 
who  have  subscribed  ;  this  Hst  I  will  send  you,  together  with  a  cheque 
for  the  balance  I  have  in  hand,  in  the  course  of  a  day  or  so.    I  also 


788  ARTICLES  OF  ASSOCIATION.  [Mar.  26th, 

enclose  a  copy  of  the  letter  that  was  sent  out,  and  hope  these  will 
reach  you  in  time  to  be  placed  before  the  Council  this  evening. 
The  total  number  of  Students  who  have  subscribed  is  644,  although 
included  in  this  number  are  some  Students  who  are  studying  electrical 
engineering,  though  not  Student  Members  of  the  Institution.  My 
Committee  are  extremely  pleased  with  the  result  of  this  movement,  as  it 
shows  that  the  Students  recognise  the  desirability  of  a  home  for  the 
Institution. 

"  Believe  me, 

"  Very  sincerely  yours, 

"  Harold  D.  Symons." 

Donations  to  the  Library  were  announced  as  having  been  received 
since  the  last  meeting  from  Messrs.  C.  Bright,  C.  Naud,  and  Whittaker 
&  Co. ;  to  the  Building  Fundy  from  Messrs.  B.  Balaji,  S.  Evershed,  and 
J.  F.  Henderson ;  and  to  the  Benevolent  Fund  from  Mr.  W.  E.  Russell, 
to  whom  the  thanks  of  the  meeting  wer^uly  accorded. 

The  President  :  I  have  to  announce  the  result  of  a  Special 
General  Meeting  of  the  members,  held  for  the  purf)ose  of  altering 
the  Articles  of  Association.  There  were  not  many  alterations,  and 
I  will  just  explain  the  principal  ones.  The  first  is  to  give  the 
Council  the  power,  which  is  given  in  most  Societies,  of  removing 
at  their  discretion  any  one  who  is  either  a  bankrupt,  on  the  one  hand, 
or  on  the  other  hand — the' two  things  have  nothing  to  do  with  each 
other — a  felon.  That  is  a  Clause  which  is  inserted  in  most  Articles  of 
Association.  I  would  point  out  that  it  does  not  by  any  means  indicate 
that  supposing  a  man  were  unfortunately  to  become  bankrupt  he  is  to 
be  expelled  from  the  Institution,  but  supposing  a  man  were  a  fraudulent 
bankrupt,  or  it  was  supposed  that  he  was  a  fraudulent  bankrupt,  it 
might  be  very  necessary  to  remove  him  ;  but  unless  there  is  some  such 
rule  as  this  the  Council  would  not  be  able  to  do  so  without  practically 
saying  he  was  a  fraudulent  bankrupt,  and  that  might  lead  the  Institu- 
tion into  an  action  for  slander,  libel,  or  something  of  that  sort.  As  the 
Article  has  been  altered,  in  extreme  cases  it  gives  the  Council 
power  to  take  action.  The  next  alteration  is  with  regard  to  the  Vice- 
presidents.  Under  the  alteration  two  Vice-presidents  retire  every 
year.  The  idea  is  that  it  does  not  follow  that  every  Vice-president 
should  in  the  ordinary  turn  become  President.  It  is  rather  difficult 
under  the  old  rules  to  elect  a  member  a  Vice-president  unless  you 
desire  to  make  him  President  also,  and  there  are  a  great  many  people 
who  would  be  very  useful  as  Vice-presidents  without  necessarily  being 
very  well  qualified  to  serve  as  President.  It  also  gives  us  a  bigger 
number  to  choose  from.  The  arrangement  is  that  in  future  two  Vice- 
presidents  will  always  retire,  and  the  President  must  be  chosen  from 
some  one  who  has  been  a  Vice-president  ;*  so  that  a  man  who  has  once 
been  a  Vice-president  is  eligible  for  the  Chair.  By  that  means  we  will 
get  a  number  of  people,  as  it  were,  in  stock  to  choose  from,  and  it  is 
felt  that  that  will  be  better  for  the  Institution.  The  only  other 
alteration  of  any  importance  which  I  think  I  need  mention  is  that  the 


1903.]  ELECTION   OF  NEW  PRESIDENT.  789 

Associate  Members  are  now  to  have  the  power  of  voting  with  the 
Members  in  any  important  matter,  such  as  altering  the  Articles  of 
Association,  or  anjrthing  of  that  kind.  The  Council  feel  that  the 
Associate  Members  and  the  Members  only  differ  in  degree,  and  that 
they  ought  to  be  one  body.  The  last  alteration  is  a  matter  of  form, 
which,  I  believe,  is  legally  unnecessary ;  it  provides  that  every  new 
member  shall  promise  to  agree  to  the  rules  of  the  Institution,  and 
so  on. 

As  I  mentioned  at  our  last  meeting,  it  is  very  important  that  the 
Institution  should  have  a  President  who  should  not  only  take  charge  of 
the  Institution  during  the  time  of  the  International  Telegraph  Congress 
which  is  to  be  held  in  London,  but  should  also  be  in  the  Chair  early 
enough  to  make  his  arrangements  for  taking  over  the  control  of  the 
Institution  during  the  whole  time.  I  sent  in  my  resignation,  as  I  said 
I  would,  and  the  Council  have  elected  Mr.  Gray  to  take  the  place 
of  President.  I  can  only  say  that  I  have  the  greatest  pleasure  in 
resigning  in  favour  of  Mr.  Gray.  Mr.  Gray  will  now  have  time  to 
organise  the  entertainments  of  the  Congress  in  a  way  that  I  feel  sure 
you  will  find  will  do  great  honour  to  the  Institution.  I  have  great 
pleasure  in  resigning  in  favour  of  Mr.  Gray,  and  I  will  now  ask  him  to 
take  the  Chair. 

[Mr.  Swinburne  then  vacated  the  Chair,  which  was  taken  by 
Mr.  R.  K.  Gray.] 

Mr.  J.  Gavey  :  Gentlemen,  before  the  new  President  addresses  you, 
I  should  like,  if  you  will  allow  me,  to  intervene  with  a  few  remarks. 
The  post  of  President  of  this  Institution  confers  high  honour  on  the 
holder,  for  he  is  for  the  time  being  the  head  of  our  profession.  It  also 
entails  very  onerous  labours,  labours  of  which,  perhaps,  only  those  who 
are  on  the  Council,  or  who  have  served  on  the  Council,  are  really  good 
judges.  You  are  able  to  appreciate  the  able  manner  in  which  the 
past  President  has  upheld  the  high  traditions  of  his  office  in  presid- 
ing over  your  meetings.  I,  as  a  member  of  the  Council,  can  testify 
to  the  great  business  aptitude  with  which  he  has  conducted  the 
deliberations  of  the  Council,  and  with  which  he  has  managed  the  affairs 
of  your  Institution.  Gentlemen,  great  professional  ability  or  great 
business  acumen  compel  admiration,  but  there  are  other  qualities  which 
command  esteem  and  regard;  and  personally  I  can  say  that  your 
retiring  President  has,  during  his  year  of  office,  shown  such  an  amount 
of  tact  and  courtesy  in  dealing  with  the  affairs  of  the  Institution,  that  he 
leaves  behind  him  a  body  of  men,  who,  I  venture  to  say,  consider  them- 
selves his  personal  friends.  If  you  want  an  illustration  of  the  tact  and 
courtesy  with  which  he  has  dealt  with  his  duties,  I  need  only  call  your 
attention  to  the  graceful  and  generous  manner  in  which  he  has  retired 
before  the  expiry  of  his  period  of  office,  in  order  that  his  successor  may 
have  the  fullest  opportunity  of  organising  the  reception  of  the 
International  Telegraph  Conference  in  the  manner  most  satisfactory 
to  himself  and  to  the  best  advantage  of  the  Institution.  I  have  much 
pleasure  in  proposing  a  very  hearty  vote  of  thanks  to  the  retiring 
President. 

Mr.  W.  H.  Patch  ELL  :  Gentlemen,  the  duty  which  devolves  upon 


740  CONSTABLE   AND   FAWvSSETT  [Mar.  26th, 

me  to  night  should  properly  devolve  upon  one  of  the  Vice-presidents, 
but  they  are  unfortunately  absent  owing  to  the  Dinner  to  Sir  William 
White,  which  has  called  for  the  personal  service  of  them  all.  Our  past 
President — I  am  sorry  to  have  to  call  him  so  so  soon— ought  to  have 
been  there  also,  and  it  is  only  another  instance  of  the  courtesy  with 
which  he  has  invariably  treated  us  here  that  he  has  foregone  so  much 
of  the  dinner,  although  he  hopes  presently  to  get  in  for  the  ices. 
Mr.  Gavey  has  told  you  something  about  our  past  President's 
handling  of  the  Council,  and  you  have  seen  for  yourselves  the  way 
in  which  he  has  handled  these  meetings.  As  a  specimen  of  his 
tact,  I  need  only  refer  to  the  fact  that  he  had  hardly  got  into  the 
Chair  when  he  had  to  head  the  deputation  to  the  Board  of  Trade,  and 
I  think  the  handling  of  that  deputation  was  just  a  masterpiece  of 
diplomacy.  No  words  from  me  could  give  you  any  higher  opinion  of 
Mr.  Swinburne  than  he  has  earned  for  himself.  He  is  only  a  young 
man,  and  I  hope  we  may  live  to  see  him  serve  us  again  when,  instead 
of  having  an  abbreviated  year  of  office,  I  hope  we  may  be  able  to  give 
him  a  leap  year. 

The  resolution  was  carried  with  acclamation. 

Mr.  J.  Swinburne  :  Mr.  President  and  gentlemen,  it  is  very 
difficult  indeed  for  a  man  to  reply  to  such  very  kind  speeches  as  I  have 
heard  to-night,  and  to  reply  after  a  vote  of  thanks  has  been  carried  in 
the  way  in  which  you  have  carried  this  one.  I  can  only  say  that  being 
your  President  is  the  greatest  honour  that  can  be  conferred  on  any 
member  of  the  profession.  But  in  my  case  I  have  felt  that  it  was  not 
only  a  great  honour  but  an  immense  pleasure.  I  have  had  nothing  but 
pleasure  throughout  the  time  I  have  had  the  honour  of  being  your 
President,  I  am  very  sorry  to  resign  in  one  sense,  and  in  another  sense 
I  am  very  glad  indeed,  because,  though  I  have  enjoyed  my  time  very 
much,  and  everybody  has  treated  me  with  the  greatest  kindness,  I 
cannot  help  feeling  that  in  Mr.  Gray  you  have  a  more  experienced 
man,  a  man  who  will  be  about  the  best  President  you  possibly  could 
have.     I  thank  you,  gentlemen. 

The  President  (Mr.  R.  K.  Gray)  said:  Gentlemen>  before  pro- 
ceeding to  the  discussion  of  the  papers  that  we  have  before  us 
to-night,  I  desire  to  say,  in  as  few  words  as  possible,  that  I  appre- 
ciate very  much  the  honour  which  has  been  conferred  upon  me  by 
the  Council,  and  I  sincerely  hope  I  shall  be  able  to  follow  the  tradi- 
tions of  my  predecessors  in  this  Chair.  I  will  not  occupy  your  time 
any  longer,  except  to  tender  you  my  best  thanks  for  the  very  kind  way 
in  which  you  have  received  the  announcement  which  Mr.  Swinburne 
has  made  to  you. 

Resumed  Discussion  on  Papers  on  "  Distribution  Losses  in 
Electric  Supply  Systems,"  by  A.  D.  Constable,  A.M.I.E.E., 
AND  E.  Fawssett,  A.I.E.E.,  and  '*  A  Study  of  the  Phenomenon 
OF  Resonance  in  Electric  Circuits  by  the  Aid  of  Oscillo- 
grams," by  M.  B.  Field,  M.I.E.E.,  A.M.I.C.E. 

Mr.  Mr.  T.   H.   MiNSHALL  :  I   think  the  peculiar  value   of   these  two 

"*  papers  which   arc   before   us  to-night,  dealing  as  they  do   with  the 


1903.]  AND   FIELD  :   DISCUSSION.  741 

oscillograph,  is  not  so  much  the  accuracy  of  the  results  which  are  given,   Mr. 

although  many  of  those  are  very  interesting,  but  the  number  of  new 

suggestions  which  they  make  to  men  engaged  in  practical  engineering. 

Mr.  Constable's  paper,  together  with   the  diagrams  which  are  given, 

has  come  in  a  sense  as  a  revelation  to  a  great  many  station  engineers. 

A  good  many  of  us  did  not  realise,  until  the  oscillograph  was  made 

a  practical  instrument,  what  extraordinary  wave-forms  we  have  to  deal 

with ;   and  when  one  sees  some  of  the  very  peculiar  shapes  which 

are   shown  in  some  of  the  tables,  more  especially  in  Table  No.  4, 

one  is  not  at  all  surprised  at  almost  any  form  of  resonance  effect 

or  breaking-down  effect  which  one  hears  of  in  actual  practice.    There 

are   several  points  that    occur    to    me  which   have    not  had  much 

attention  drawn  to  them  before.    One  of  those  is  the  question  of  the 

enormous  loss  which  goes  on  in  all  central  stations.    One  does  not 

realise  that  actually  25  per  cent,  of  the  total  output  of  a  station  is,  at 

the  present  time,  lost.    Of  course  it  must  be  borne  in  mind  that  of  that 

loss  a  great  deal  occurs  at  the  top  of  the  load,  and  that  hence  the  cost 

of  generation  of  those  units  must  be  taken  as  the  maximum  possible. 

Taking  these  units  given  in   the   paper,  and  allowing  the  average 

cost  of  generation  of   the  total  of   173,000  units,  we  get    between 

£"200  and  £'yyo  a  year  actually  lost;    if    you    can    save    them,  or 

prevent  them  going  in  any  way,  it  is  all   profit.     I   do  not  know 

that  there  are  any  other    points  that  occur    to   me  in   connection 

with  the  first  part  of   the  paper.    The  dielectric  hysteresis  is  the 

part  which  appeals  to  me  as  the  most  interesting,  although  possibly 

it   is  not  the  one  of  the  greatest  practical  importance.    This  paper 

originated  with  some   experiments  that  Mr.  Constable  made  for  me 

in  connection  with  the  discussion  on  Mr.  Mordey's  most  interesting 

paper  last  year.    Members  may  recollect  that  in  that  paper  Mr.  Mordey 

showed  some  results  with  a  power-factor  of  the  order  of  o'l.    The 

Institution  at  the  time  as  a  whole,  I  think,  did  not  entirely  agree  with 

those  figures,  and  we  made  some  experiments  at  Croydon  to  see  if  such 

a   thing  were  possible.      It  so  happened   that    the   experiments  we 

conducted  were  not  on  a  paper  cable,  but  on  a  vulcanised  bitumen 

cable,  and  we  got  results  almost  exactly  agreeing  with  Mr.  Mordey's. 

I  do  not  pretend  that  anybbdy  believed  them  ;  so  we  spent  some  time 

and  trouble  since  then  in  attempting  to  produce  the  results  by  several 

methods.     I  think  Mr.  Constable  shows  here  fairly  conclusively  that 

with   a  cable  of   this  peculiar  construction  and  material,  it  is  quite 

possible  to  get  a  power-factor  of  the  order  of  o*i.    As  a  matter  of 

£act,  when   he  comes  to  deal  with  jute  cables  and  paper  cables,  of 

course  then  the  results  which  he  obtained  are  more  in  accordance  with 

those  which  were  obtained  by  so  many  investigators  last  year.    There 

is  no  doubt,  I  think,  that  the  ordinary  power-factor  of  the  ordinary 

paper  cable  is  of  the  order  of  001  or  0*02.     I  do  not  think  it  would 

be  very  much  higher,  although  some  of   the  jute   cables  seemed  to 

go  as  high  as  0*03,  but   I  should  think  3  per  cent,  is  the  maximum 

power-factor  which  is  obtained  from  any  of  these  cables  in  commercial 

use.    Mr.  Constable  gives  on  page  713  a  very  interesting  resume  of 

the  various  methods  \vhich  are  applicable  to  a  measurement  of  this 


Minshall. 


742  CONSTABLE   AND   FAWSSETT  [Mar.  26th, 

Mr.  kind.     It  is  very  important  indeed  that  one  should  clearly  realise  the 

"****"*       great  difficulty  there  is  in  conducting  investigations  into  what  he  has 
called  dielectric  hysteresis.    The  five  methods  he  has  given  here  are  all 
of  them  to  a  certain  extent  practical,  provided  that  3rou  have  sufficient 
time  and  apparatus  at  your  disposal.    The  first  one  certainly  appears  to 
be  one  of  the  best.    When  I  was  in  America  last  year  I  discussed  the 
matter  at  some  length  with  Mr.  Steinmetz  and  Mr.  Berg,  and  they 
were  of  the  opinion  that  they  would  use  the  one  the  authors  used  ; 
but  when  I  showed  them  some  of  the  wave-forms  in  the  diagrams  on 
page  711,  they  agreed  that  it  was  not  perhaps  such  a  good  method  to 
use  as  they  had  previously  thought.     My  own   conclusion  is  that  if 
it  is  not  possible   to  use  a  calori metric  method,    the  only  method 
on   which    one  could    really   rely   with   bad   wave-forms    is    No.  3, 
that  is,  the  direct  measurement    of    increased  power    necessary  to 
drive  an  alternator   when   a  cable    is  switched  on.     Of    course    at 
the  first  glance  it  appears  as  if  the  measurement  to  be  made  is  so 
extremely  minute  that  it  is  impossible  to  measure  it ;  but  a  small  motor 
alternator,  carefully  driven,  with  the  supply  at  the  direct-current  end 
measured  on  a  potentiometer,  would  enable  one,  on  a  long  cable,  to 
get  results  of  very  considerable  accuracy.    The  difficulty  is  that  the 
wave-form  of  the  alternator  itself,  unless  care  be  taken,  gets  altered 
during  the  experiment ;  that  is  to  say,  you  may  have  practically  a  sine 
wave  before  you  put  the  cable  on,  and  then  immediately  you  put  it  on 
you  get  one  of  the  forms  shown  in  Table  4.    I  know  that  Mr.  Constable 
took  very  great  efforts  to  get  over  that.     He  took  a  motor  alternator 
and  loaded  it  up  with  30  kilowatts,  and  switched  a  cable  on  the  losses 
in  which  added   i    kilowatt   extra  load,  hoping    thereby    he    would 
preserve  the    same    wave-form    as  before.      But    he    found    it    was 
impossible  to  be  quite  sure,  and  I  am  afraid  the  results  he  obtained 
from  that  are  more  or  less  negative.     If  one  could  get  a  sine-wave 
machine,  and  potentiometers  of  sufficient  accuracy,  it  is  a  method 
which  promises  a  good  deal  in  the  hands  of  a  really  careful  investigator. 
The  author  has  not  drawn  attention  to  one  very  interesting  experiment 
which  we  made  some  time  ago  at  Croydon  to  show  that  the  current, 
and  even  sometimes,  owing  to  the  alteration  in  wave-form,  the  watts 
flowing  into  a  cable  on  open  circuit  may  be  actually  greater  than  when 
some  load   is  put  on   at  the  end.    We  took  a  long  cable  of  about 
7,000  yards,  put  on  an  alternator,  and  measured  the  capacity  current 
flowing  into  the  cable.    We  then  added  a  couple  of  transformers, 
open-circuited,  whose  core  losses  amounted  to  two  kilowatts,  the  result 
being  that  the  current  entering  the  cable  was  measurably  smaller  than 
before.    That  has  been  repeated  a  good  many  times,  but  I  do  not 
think  he  draws  attention  to  it  anywhere  here.     It  merely  shows  that  if 
properly  arranged  the  capacity  of  a  cable  on  a  large  net  work  may  be 
of  advantage  rather  than  otherwise.    As  a  matter  of  fact   it  is  not 
actually  so  deleterious  to  the  supply  as  possibly  is  sometimes  imagined. 
I   do  not  think  there  are  any  other  points  that  I  remember  at  the 
time  in   that  connection,  but   I   should    like  to  refer  to    a    remark 
made  in  connection  with   telephones.    We  had   much  trouble  from 
Sydenham  and  Croydon  and  on  to  Purley  with  the  telephone  cables ;  we 


1903.] 


AND   FIELD;    DISCUSSION. 


743 


were  a  great  nuisance  to  the  National  Company,  and  a  great  deal  more  Mr. 
nuisance  to  ourselves.  Eventually  the  manager  of  the  National  Tele- 
phone Company  in  that  neighbourhood  and  myself  investigated  the 
matter  at  some  length  and  came  to  the  conclusion  that  you  can  take 
a  concentric  cable,  put  it  in  a  lead  sheath,  in  an  iron  trough,  and 
lay  another  cable  by  the  side  of  it  also  in  a  lead  sheath,  and  still 
get  any  amount  of  stray  field,  or  what  appears  to  be  stray  field  :  you 
can  get  enough  humming  to  make  it  practically  impossible  to  hear 
on  the  telephone.  Some  people  say  it  is  leakage,  others  static  effect. 
We  investigated  very  carefully  to  find  if  it  was  leakage,  but  we  satisfied 
ourselves  entirely  that  it  was  not  electrical  leakage  at  all.  When  the 
current  increased  in  the  evening  the  sound  was  very  greatly  increased 
too ;  in  the  day  time,  when  there  was  very  little  current  flowing  in 
the  cable,  there  was  very  little  noise  in  the  telephone.  We  came 
finally  to  the  conclusion  that  the  only  really  satisfactory  way  of 
running  telephone  cables  near  high-tension  cables  was  not  to  trust  to 
any  sheathing  whatever,  but  to  increase  the  distance.  I  shall  be  glad 
to  hear  the  experience  of  other  engineers  on  that  point,  because  it  is 
one  which  caused  us  a  great  deal  of  trouble,  I  will  not  detain  the 
Institution  by  drawing  attention  to  the  number  of  other  uses  which  the 
oscillograph  is  going  to  have  in  the  future  ;  but  there  is  one  in 
particular  which  appealed  to  me,  namely,  that  in  specifying  high- 
tension  machinery  it  is  now  becoming  customary  to  specify  the  wave 
form  of  generator,  rotary,  or  motor  generator  as  the  case  may  be.  One 
has  not  only  to  specify  voltage,  and  that  sort  of  thing,  but  one  has  to 
say  what  sort  of  wave  the  machine  is  to  give.  Hitherto  it  has  been 
easy  to  specify,  but  it  has  been  difficult  to  see  that  you  were  getting 
what  you  wanted.  Here  you  get  an  opportunity  of  seeing  that  the 
contractor  is  complying  with  a  specification,  an  opportunity  which 
hitherto  has  been  impossible.  I  think  every  alternate-current  station 
engineer  should  get  his  directors  to  agree  that  the  sum  expended  on 
this  little  apparatus  is  very  well  spent  indeed. 

Mr.  W.  DuDDELL  :  Messrs.  Constable  and  Fawssett  have  used  three 
different  methods  to  determine  the  losses  in  their  cables,  viz. : — 
(i)  The  wattmeter  method. 

(2)  I'he  wave-form  method. 

(3)  The  extra  power  required  to  drive  an  alternator  method. 
Of  these  methods  I  have  no  doubt  that  the  wattmeter  method  is  one 

of  the  best,  if  not  the  best.  If  a  suitable  wattmeter  and  suitable  scries 
resistances  for  the  pressure  coil  are  used,  accurate  results  can  be 
obtained,  in  spite  of  the  wave-forms  being  as  irregular  as  those  shown 
in  Mr.  Constable's  paper.  I  hope  that  Diagram  4,  which  shows  the 
wattmeter  connection,  is  wrong.  In  it  the  pressure  coil  of  the  watt- 
meter is  shown  connected  direct  to  a  resistance  marked  R4,  with  no 
non-inductive  resistance  in  series  with  it.  If  that  was  really  the  case, 
very  large  errors  were  introduced.  Judging  from  the  oscillograph 
connections,  this  appears  to  have  been  the  case,  for  the  terminals  of 
the  resistance  R4  are  shown  connected  straight  to  the  oscillograph, 
which  only  requires  i  volt  to  operate  it. 

From  the  text  it  seems  as  if  they  used  some  resistance  in  series 
Vou  8Z  49  (Rev.) 


Mr.  Duddcll. 


744  CONSTABLE  AND  FAW8SETT  [Mar.  26th, 

Mr.  Duddeu.  with  the  pressure  coil  of  the  wattmeters  which  they  have  omitted  to 
show.  In  any  case  it  would  be  of  great  interest  to  know  the  values  of 
the  resistance,  self-induction,  and  capacity  of  the  pressure  coil  circuits 
for  each  of  the  wattmeters  they  used.  I  hope  the  authors  will  be  able 
to  give  these  figures,  as  they  will  enable  a  more  accurate  estimate  of 
the  obtainable  acciu"acy  to  be  formed. 

Coming  next  to  the  methods  of  calibrating  the  wattmeters  on  power 
factors  less  than  unity,  they  state  that  they  calibrated  them  with  a 
lagging  current  by  using  a  choking  coil.  If  the  choking  coil  is  properly 
constructed,  there  is  not  much  difficulty  in  calculating  the  true  power 
losses  in  it.  They  also  state  that  they  obtained  a  leading  ciu-rent  having 
a  power-factor  of  0*14.  I  should  like  to  ask  them  how  they  calculated 
the  value  of  the  power-factor  in  that  case.  Diagram  No.  3  throws  no 
light  on  the  matter  whatever,  and,  as  far  as  I  can  gather,  it  is  impossible 
to  calculate  the  power-factor  unless  they  either  assume  a  pure  sine 
wave,  or  analyse  the  actual  wave  used,  and  calculate  each  term  of  the 
series  representing  the  wave-form  separately.  There  is  no  indication 
that  this  was  done.  If  the  actual  wave  used  is  that  given  in  Fig.  D., 
which  is  far  from  being  a  sine  wave,  and  if  they  assumed  a  sine  wave 
in  their  calculations,  then  the  calculation  of  the  0*14  power-factor  and 
the  calibration  of  the  wattmeters  with  leading  currents  is  inaccurate. 
I  hope  the  authors  will  explain  this  matter  fully  in  their  reply,  as  it 
afiEects  the  accuracy  of  all  their  wattmeter  measurements  of  the  cable 
losses.  I 

[Communicated  May  6th,  The  ingenious  method  described  by  Mr. 
Constable  in  his  reply  neglects  the  self-induction  of  the  fixed  coil  of  his 
wattmeter  and  assumes  the  current  A,  through  it  in  phase  with  the 
applied  volts  V.  Was  this  self-induction  negligible  compared  with  the 
resistance  ?] 

Ever  since  Mr.  Mordey's  paper,  Mr.  Mather  and  myself  have  been 
working  on  the  design  of  a  satisfactory  wattmeter  and  series  resistance, 
especially  for  use  on  very  low  power-factors,  and  we  have'  now  designed 
and  had  in  use  for  some  months  an  astatic  wattmeter  which  is  quite 
free  from  metal  parts  in  the  frame,  which  has  the  minimum  amount  of 
metal  necessary  in  the  coils,  and  which  gives  a  good  deflection,  even 
with  very  low  power-factors.  In  fact,  the  wattmeter  is  so  sensitive  that 
with  a  power-factor  of  o'l  you  get  a  complete  revolution  of  the  torsion 
head,  so  that  a  power-factor  of  o'oi  is  perfectly  easy  to  read  with  a  high 
degree  of  accuracy.  We  have  also  designed  and  constructed  special 
forms  of  resistances  for  use  in  series  with  the  pressure  coil,  for,  as  h 
well  known,  the  errors  in  these  resistances  are  very  often  very  much 
bigger  than  that  due  to  the  self-induction  of  the  pressure  coil  of  the 
wattmeter  itself.  We  have  made  numerous  experiments  to  test  the 
accuracy  of  this  wattmeter,  and  we  hope  to  have  the  opportunity  later 
on  of  describing  it  and  the  resistances.  With  regard  to  method  No.  2, 
the  wave-form  method,  it  is  not  very  suitable  for  very  irregular  wave- 
forms, unless  the  wave-forms  are  actually  photographed.  It  does  not 
suffice  to  photograph  a  mean  wave-form,  as  Mr.  Field  has  done.  You 
must  get  an  individual  pressure  curve  and  the  corresponding  current 
curve  belonging  to  it,  and  you  must  work  the  result  out  from  the 


1903.]  AND   FIELD:   DISCUSSION.  745 

contemporaneous  values  of  the  P.D.  and  current  obtained  from  those  Mr.  Duddcu. 
two  curves.  You  must  not  take  the  P.D.  curve  of  one  period  and 
integrate  with  the  current  curve  of  the  next,  nor  take  a  mean  of,  say, 
ten  P.D.  waves,  and  work  out  the  power-factor  with  the  mean  of  ten 
current  waves  ;  you  must  take  each  individual  pair  of  curves  together, 
because  they  may  vary  considerably,  I  have  on  the  table  the  apparatus 
I  use  for  obtaining  photographic  records,  which  records  the  individual 
waves  and  not  the  mean  waves,  like  the  apparatus  used  by  Mr.  Field. 
There  are  really  two  sets  of  apparatus  here.  One  is  suitable  for 
working  on  voltages  up  to  15,000  with  no  earth  connection,  the  record 
b€nng  made  either  on  a  falling  plate  or  on  a  long  length  of  film  up  to 
about  160  feet  where  many  consecutive  wave-forms  are  required.  The 
other  apparatus  is  for  short  lengths  of  film  only. 

With  regard  to  method  No.  3,  the  extra  power  required  to  drive  the 
alternator,  Mr.  Minshall  was,  I  think,  a  little  inclined  to  advocate  this 
method.  I  regret  that  he  has  done  so,  for  I  totally  disagree  with  him. 
I  have  never  been  able  to  find  any  basis  for  hoping  for  accuracy  from 
this  method.  The  efficiency  of  the  alternator  is  totally  changed  by  the 
action  of  the  capacity  current.  With  ordinary  alternators,  as  I  hope  to 
show  you  presently  on  the  screen,  the  capacity  may  produce  serious 
resonances  of  the  higher  harmonics,  and  the  effect  of  adding  the 
capacity  current  will  tend  to  excite  the  alternator,  and  will  alter  the 
efftcicncy  by  altering  the  distribution  of  losses.  I  see  no  means  of 
getting  over  this  objection.  In  fact,  sometimes  an  alternator  seems  to 
take  less  power  to  drive  it  if  the  cables  are  connected,  but  most  alter- 
nators seem  to  take  very  much  greater  power,  the  iron  losses  being 
increased  by  the  high  frequency  of  the  capacity  current. 

Turning  to  Table  No.  4  of  Messrs.  Constable  and  Fawssett's  paper, 
they  give  the  results  of  the  tests  of  five  different  cables;  by  taking 
means  of  their  figures  their  results  may  be  resumed  as  follows : — 

Cable  No.  4  power-factor    22  per  cent. 


7 

tt 

II-I             „ 

9 

it 

2-8         „ 

10 

fi 

7*3  and  2*4  per  cent 

This  latter  value,  2*4  per  cent.,  was  obtained  with  the  choker  in  parallel, 
and  is  probably  the  more  accurate,  as  the  wattmeter  was  then  working 
at  a  higher  power-factor.  For  the  last  cable.  No.  11,  they  give  two 
totally  different  sets  of  results.  The  mean  of  the  first  set,  obtained  from 
curves  E,  F,  G,  is  i'4  per  cent.,  and  the  mean  of  the  second  set,  obtained 
from  curves  I,  J,  K,  is  no  less  than  8  per  cent.  I  should  like  to  ask  them 
what  is  the  difference  between  the  tests  E,  F,  G  and  I,  J,  K.  In  one 
case  they  say  they  obtained  1*4  per  cent.,  and  in  the  other  8  per  cent. 
If  you  refer  to  the  diagrams  of  the  wave  form,  you  will  note  that  the 
first  three,  E,  F,  G,  have  a  resonance  of  the  fifth  harmonic,  and  in  the 
last  three  they  got  resonance  in  the  third  harmonic.  How  is  it  with 
the  same  cable  they  have  these  two  different  resonances  ?  Did  they 
use  a  different  alternator  in  the  two  cases,  or  different  frequency,  or 
was  there  by  any  chance  a  transformer  connected  across  the  cable  in 
the  case  of  I,  J,  K  ?    In  no  case  do  they  give  any  indication  as  to  the 


746  CONSTABLE  AND   FAWSSETT  [Mar.  3eth,i 

Mr.  Duddeu  nature  of  the  machine  and  frequency  used  in  each  test.  There  is  no 
doubt  whatever  that  the  self-induction  connected  between  the  terminals 
of  the  cable  tests  I,  J,  K  was  very  much  greater  than  in  E,  F,  G,  if  the 
frequency  was  the  same  ;  yet  they  have  accepted  the  high  loss  as  more 
probably  correct.  Taking  the  figures  for  the  five  cables,  which  are  not 
on  the  face  of  them  doubtful,  the  losses,  as  Mr.  Minshall  said,  are 
generally  under  3  per  cent.,  except  in  the  one  case  of  the  No.  7  cable. 
That  cable  appears  to  be  'a  bad  cable  as  far  as  light-load  loss  is 
concerned. 

I  have  tested  by  means  of  the  wattmeter  already  mentioned  various 
cables  belonging  to  electric  light  companies  in  and  around  Londoiu 
and  in  general  the  power-factor  has  varied  from  1-5  per  cent,  to  3  per 
cent.,  the  power-factor  differing  from  one  cable  to  the  next,  even  ^when 
they  were  very  similar  in  make  and  construction.  I  have  also  tried  the 
effect  of  varying  the  voltage  used  on  some  cables  over  a  fairly  wide 
range,  and  find,  as  Messrs.  Constable  and  Fawssett  point  out,  that  there 
seems  to  be  a  tendency  for  the  power-factor  to  increase  with  increase 
of  the  applied  potential  difference.  The  effect  of  a  change  of  the 
applied  wave-form  due  to  resonance  of  one  of  the  harmonics  has  been 
to  make  the  power-factor  larger  when  the  resonance  occurred  than  when 
there  was  no  resonance,  evidently  due  to  the  increased  value  of  the 
maximum  instantaneous  E.M.F.  In  all  the  tests  I  have  so  far  made — 
and  they  have  been  made  under  ordinary  working  conditions,  with  the 
cables  connected  up  to  the  switchboards  exactly  as  used,  and  no  allow- 
ance being  made  for  any  C'R  losses  due  to  the  capacity  current — I  have 
never  come  across  a  cable  giving  a  power-factor  above  3*5  per  cent, 
except  the  No.  7  cable  at  Croydon,  which  I  once  tested,  and  I  then  had 
doubts  as  to  the  accuracy  of  my  own  test,  as  I  stated  at  the  time,  as 
during  the  test  there  appeared  to  be  such  a  violent  resonance  that  I 
could  distinctly  hear  the  resistances  in  series  with  the  volt  coil  of  the 
Swinburne  wattmeter  I  was  using  giving  a  brush  discharge,  though  the 
R.M.S.  voltage  was  only  2,000  volts.  I  still  feel  that  this  No.  7  cable 
should  be  further  tested  to  find  out  the  true  cause  of  the  great  loss  in 
it,  whether  it  be  real  or  apparent.  Messrs.  Constable  and  Fawssett 
suggest  that  it  may  be  caused  by  a  magnetic  field,  though  this  present> 
serious  difficulties.  I  asked  Mr.  Fawssett  to  make  some  further  exf)eri- 
ments  on  this  point,  the  results  of  which  he  will  no  doubt  tell  us.  The 
noise  in  the  telephone  referred  to  may  well  be  due  to  leakage  from  the 
outer  to  earth,  and  would  increase  with  the  load. 

Messrs.  Constable  and  Fawssett's  paper  strengthens  the  conclusion 
that  it  is  quite  possible  to  obtain  commercially  cables  with  a  power- 
factor  less  than  3  per  cent.,  and  that  therefore  the  danger  pointed  out 
in  Mr.  Mordey's  paper  of  the  large  power  schemes  being. crippled  by 
the  light-load  losses  in  the  cables  themselves  is  not  at  all  serious,  and  I 
would  suggest  that  we  may  take  warning  from  Croydon  and  avoid 
cables  having  such  absurdly  high  losses  as  their  No.  7.  V.B.  cable 
appears  to  have.  Taking  Messrs.  Constable  and  Fawssett's  tests  of  the 
No.  7  cable  as  correct  at  a  i^.  per  unit,  £^0  per  annum  of  the  rate- 
payers' money  is  being  wasted  in  warming  the  cable  instead  of  a 
quarter  that  amount,  and  probably  ijd.  per  unit  is  an  under-estimate 


J-] 


AND   FIELD:    DISCUSSION. 


747 


Mr.  Duddell. 


Fig.  B. — Alternator  and  Cables,  Normal  Speed. 


Fi(i.  C. — Alternator  and  Cables,  8  per  cent.  Over  Speed. 


Fkj.  D. — Alternators  and  Cables,  26  per  cent.  Umier  Speed. 
Scale':  i  mm.  =  458  volts. 


748  CONSTABLE   AND    FAWSSETT  [Mar.  26th, 

Mr.  Duddeii.  of  the  cost  of  producing  the  power.  With  regard  to  No.  12  cable, 
which  I  believe  includes  most  of  these  other  cables,  if  you  take  the 
total  losses,  901,  you  will  find  it  is  very  little  bigger  than  the  6oi  taken 
in  No.  7,  so  that  how  it  includes  the  high  losses  in  No.  1 1  I  do  not 
understand. 

Turning  to  Mr.  Field's  valuable  paper  on  the  resonance  question,  I 
do  not  think  that  he  has  laid  sufficient  stress  on  the  dangers  to  the 
insulation  due  to  these  resonances  of  the  higher  harmonics. 

Out  of  four  large  plants  I  have  recently  tested,  three  suffered 
seriously  from  resonances,  and  Mr.  Field  and  Messrs.  Constable  and 
Fawssett  show  us  that  both  Glasgow  and  Croydon  do.  These  reso- 
nances not  only  strain  unnecessarily  the  insulation  of  the  cables ;  they 
also  reduce  the  efficiency  of  the  machines,  make  the  regulation  bad  and 
the  working  of  motors  difficult. 

Before  proceeding  I  will  define  the  term  form  factor  as  the  ratio 

maximum  instantaneous  value  .  ,  i.        r  1  ^    * 

-  ,-r~i^-^ , for  any  wave-form,  a  most  useful  factor 

R.M.S.  value  -^ 

which  gives  a  measure  of  the  strain  on  the  insulation  due  to  the  wave- 
form. 

I  have  to  thank  the  Kensington  and  Knightsbridge  Company  for 
allowing  me  to  show  some  resonances  obtained  on  their  circuits  which 
will,  I  hope,  exemplify  the  danger  to  insulation  due  to  resonances.  In 
each  case  the  R.M.S.  voltage  is  the  same,  viz.,  5,000.  Fig.  A  is  the  open 
circuit  wave-form  of  the  one  of  their  alternators ;  the  maximum  volts 
are  1*45  times  the  R.M.S.  volts,  or  in  other  words  the  form  factor  is  1*45, 
about  the  same  as  for  a  sine  wave.  Fig.  B  is  the  P.D.  wave  form  of  the 
same  alternator  with  some  cables  connected  which  were  on  open 
circuit,  the  alternator  running  at  normal  speed  ;  the  form  factor  is  i*67. 
If,  however,  the  speed  of  the  alternator  increases  to  only  8  per  cent 
above  the  normal,  a  resonance  of  the  seventh  harmonic  occurs  (Fig.  C.) 
and  the  form  factor  increases  to  174.  On  the  other  hand,  if  the  machine 
is  allowed  to  slow  down  to  26  per  cent,  under  normal  speed,  a  reso- 
nance of  the  fifteenth  harmonic  takes  place  (Fig.  D),  and  the  form  factor 
rises  to  I  •94.  This  shows  that,  with  a  constant  excitation,  lowering  the 
speed  of  the  alternator  may  increase  the  strain  on  the  insulation.  A 
cable  should  never  be  energised  by  raising  the  speed  of  the  alternator 
after  exciting  the  latter,  for  fear  of  passing  through  dangerous 
resonances  ;  the  alternator  should  be  run  up  to  correct  speed  first,  and 
then  the  excitation  should  be  gradually  raised. 

In  some  other  stations  I  have  known  the  form  factor  to  increase  to 
as  high  as  2*2  ;  thus,  supposing  10,000  R.M.S.  volts  was  applied  to  the 
cable,  the  maximum  instantaneous  voltage  would  be  no  less  than 
22,000  volts,  or,  due  to  the  resonance,  the  cable  would  be  strained  with 
as  high  a  maximum  voltage  as  is  given  by  a  sine  wave  having  a  R.M.S. 
value  of  15,500  volts,  so  that  a  cable  designed  to  work  at  10,000  volts  on 
a  sine  wave  might  frequently  be  strained  55  per  cent,  in  excess,  due  to 
a  resonance  of  one  of  the  upper  harmonics.  I  think  that  cable  makers 
have  in  some  cases  been  unjustly  blamed  for  failures  due  to  resonance. 
These  resonances  are  a  frequent  cause  of  the  failure  of  E.S.  voltmeters. 
J t  is  to  b^  noted  that  these  high  peaks  on  the  P.D.  wave  mentipoed  do 


1903.]  AND   FIELD  :    DISCUSSION.  ,  749 

not  show  on  the  station  voltmeter  which  reads  the  R.M.S.  value,  so  the  Mr.Duddeii. 
cn^neer  in  charge  has  no  idea  how  serious  the  strain  on  his  apparatus 
is.  It  will  be  said  that  the  ordinary  rules  of  testing  to  twice  the  working 
pressure  allows  for  the  above  strains.  But  this  is  not  the  case,  as  the 
whole  of  that  margin  and  more  is  required  to  allow  for  the  strains  due 
to  oscillations  without  its  being  reduced  in  any  way  due  to  resonances. 
I  have  calculated  the  form  factors  for  some  of  the  wave  forms  in 
Messrs.  Constable  and  Fawssett's  paper  : — 


Curve  A. 

189 

Curve  E. 

197 

Curve  I. 

17s 

„      B. 

1-88 

,,      F. 

1-96 

..      J- 

172 

„    c. 

r8o 

..      G. 

193 

..     K. 

£•69 

,.      D. 

'•53 

„      L. 

185 

The  difference  between  the  form  factors  of  curves  E,  F,  G  and  of 
curves  I,  J,  K,  which  are  for  the  same  cable,  No.  11,  show,  as  I  h;ive 
already  mentioned,  that  the  conditions  under  which  these  tests  were 
made  were  evidently  very  different. 

I  think  the  above  values,  which  are  in  no  way  exceptional,  show 


Fig.  E. — Converter  ;  Effect  of  Sparking  at  Brushes  on  Direct- Current  Side. 

how  very  serious  the  dangers  due  to  resonances  of  the  higher  harmonics 
are  in  practice. 

Mr.  Field  has  referred  to  ripples  on  the  D.C,  side  of  a  rotary 
converter.  I  should  like  to  draw  attention  to  the  irregularities  which 
sparking  at  the  brushes  of  a  converter  may  produce  in  the  P.D.  wave- 
forms on  the  alternate-current  side. 

Fig.  E  shows  the  two  P.D.  waves  of  a  small  two-phase  converter 
which  was  allowed  to  spark  at  the  commutator. 

The  irregularities  in  both  the  P.D.  waves  due  to  this  sparking  are 
very  marked.  It  seems  to  me  that  these  high  frequency  ripples  might 
easily  be  resonated  and  lead  to  very  serious  difficulties  and  dangers  in 
working,  so  that  a  converter  which  was  working  perfectly  satisfactorily 
might,  by  being  allowed  to  spark  at  the  brushes,  cause  a  serious 
resonance  with  the  attendant  dangers  to  itself  and  the  rest  of  the  plant. 

Prof.  A.  Hay  :  In  connection  with  Messrs.  Constable  and  Fawssett's  Prof-  Hay. 
paper,  I  should  like  to  make  a  few  remarks  with  regard  to  the  alleged 


750  CONSTABLE   AND    FAWSSETT  [Mar.  26th. 

Prof.  Hay.  magnetic  field  which  exists  around  the  concentric  cable.  It  is  very 
difficult  to  believe  that  such  a  field  can  exist,  and  the  only  way  in  which 
it  can  possibly  be  brought  about  is  by  a  slight  excentricity  in  the  inner 
conductor  of  the  cable  ;  a  large  amount  of  excentricity  is  of  course  out 
of  the  question.  It  seems  to  me  that  the  experiments  with  telephones 
prove  nothing  at  all,  because  there  is  a  much  simpler  explanation, 
namely,  a  purely  electrostatic  disturbance.  If  you  consider  the  outer 
conductor  of  the  cable  and  suppose  that  it  is  conveying  an  alternating 
current,  you  will  have  a  periodic  rise  and  fall  of  potential  at  each  end 
of  the  cable.  You  have  your  pilot  wire  in  the  same  trough  near  the 
outer  conductor,  and  you  are  bound  to  get  a  considerable  amount  of 
electrostatic  action  between  the  pilot  wire  and  the  outer  conductor  of 
the  concentric  cable.  Such  disturbances  are  well  known  to  telephone 
engineers,  and  I  think  that  there  is  no  doubt  the  effects  observed  are 
due  entirely  to  purely  electrostatic  causes  and  not  to  electro-magnetic 
disturbances,  as  has  been  suggested  by  the  authors.  In  connection 
with  the  remarks  made  by  Mr.  Duddell,  I  am  sorry  to  note  that  he  is 
introducing  a  new  term  and  using  an  old  name  for  it.  He  speaks  of 
the  form  factor  of  the  wave-form.  As  a  matter  of  history,  I  believe  I 
am  right  in  saying  that  Dr.  Fleming  was  the  first  to  introduce  certain 
terms  which  had  definite  reference  to  the  wave-forms  of  alternating 
currents  and  P.D.s.  The  two  terms  introduced  by  him  were  the  form 
factor y  which  he  defined  as  the  ratio  of  the  R.M.S.  to  the  mean  value  of 
the  wave,  and  the  amplitude  factory  which  denoted  the  ratio  of  the 
R.M.S.  to  the  maximum  value.  Dr.  Fleming's  amplitude  factor  is  thus 
the  reciprocal  of  Mr.  Duddell's  form  factor,  and  Dr,  Fleming's  form 
factor  is  something  totally  different.  As  the  term  form  factor  has  been 
used  by  both  English  and  continental  writers  in  the  meaning  given  to 
it  by  Dr.  Fleming,  I  hope  Mr.  Duddell  will  try  and  invent  some  other 
suitable  term  for  the  ratio  of  the  maximum  to  the  R.M.S.  value. 

Referring  next  to  Mr.  Field's  paper,  I  wish  to  point  out  that  from 

equation  (9)  and  the  further  condition  K  =  ^  it  clearly  does  not  follow 

that  the  arrangement  of  branched  circuit  indicated  will  be  equivalent 
to  a  simple  non-inductive  resistance  of  r  ohms  for  all  frequencies,  since 
the  equation  (9)  involves  the  frequency. 

[Note  added  later.    On  investigating  the  matter  fully,  I  find  that 

balance  for  all  frequencies  may  be  obtained  by  making  K  =  ^,   and 

that  this  is  the  sole  condition  required  ;  Mr.  Field's  equation  (9)  is  not  a 
necessary  condition.  Thus  Mr.  Field's  final  result  is  correct,  although 
his  manner  of  arriving  at  it  is  entirely  erroneous.] 

I  must  further  tax  Mr.  Field  with  using  terms  which  are  out  of  date. 
He  speaks  of  ohmic  resistance,  I  should  like  to  ask  Mr.  Field  whether 
there  is  such  a  thing  as  a  resistance  which  is  not  ohmic.  Then  he 
speaks  of  the  secohm.  I  should  like  to  know  what  the  secobm  is.  It 
is  to  be  regretted  that  Mr.  Field  does  not  see  fit  to  use  the  modern  unit 
of  self-inductance — the  henry.  Again,  Mr.  Field  uses  the  term  "  self- 
induction  "  in  two  totally  different  senses.  I  should  like  to  suggest  the 
^se  of  thp  term  "  leakage  self -inductance/'  and  then  nobody  can  possibly 


1903.]  AW)   FIELD:    DISCUSSION.  761 

make  a  mistake ;  the  matter  is  perfectly  clear.    If  you  define  self -indue-  P">f-  Hay. 
tion  in  one  way  and  then  proceed  to  use  it  in  a  totally  different  sense, 
confusion  is  bound  to  result. 

In  Part  2  of  the  paper  Mr.  Field  states  that  he  is  perfectly  aware 
that  the  peculiar  effects  obtained  during  the  charging  of  a  condenser 
are  treated  mathematically  in  the  various  text-books  on  the  subject, 
impl3ring  that  the  subject  had  not  been  dealt  with  experimentally 
before.  If  Mr.  Field  is  interested  in  the  subject>  I  can  give  him 
references  to  several  papers  in  which  curves  similar  to  those  he  gives 
are  plotted  to  scale,  showing  not  only  the  oscillations  of  the  charging 
current  of  the  condenser,  but  also  the  abnormal  rises  of  potential  which 
are  produced. 

[Note  added  later.  The  references  are  : — Phil.  Mag,  for  1892 
(voL  xxxiv.,  p.  389) ;  Proc,  Roy.  Soc.  for  1893  (vol.  54,  p.  7) ;  The 
Electrician  for  1895  (vol.  xxxv.,  p.  840.] 

In  connection  with  the  higher  harmonics  of  alternating  E.M.F. 
waves,  it  may  be  interesting  to  refer  to  an  arrangement — recently 
patented  by  Arnold,  Bragstad,  and  la  Cour — in  which  the  property 
possessed  by  the  third  harmonic  in  a  three-phase  system  is  utilised. 
It  is  not  difficult  to  show  that  there  can  be  no  third  harmonic  in  the 
P.D.  wave  between  any  two  wires  of  a  three-phase  system  supplied  by 
a  star-connected  three-phaser ;  for,  since  a  phase-displacement  of 
i  period  for  the  main  wave  corresponds  to  a  phase-displacement  of  a 
whole  period  for  the  third  harmonic,  the  E.M.F.s  corresponding  to  this 
harmonic  will  at  every  instant  be  equal  and  all  act  either  towards 
or  else  away  from  the  neutral  point.  But  if  the  neutral  points  of 
generator  and  motor  or  transformer  (star-connected)  be  connected 
through  a  lamp  or  motor  load,  a  path  will  be  provided  for  the 
high-frequency  current  corresponding  to  the  third  harmonic. 
Such  an  arrangement,  originally  proposed  by  Bedell,  would,  how- 
ever, be  practically  useless  on  account  of  the  choking  effect  of  the 
motor  or  transformer  circuits.  Arnold  and  his  co-workers  overcome 
the  difficulty  by  distributing  the  winding  corresponding  to  each 
phase  over  two  cores,  the  connections  being  such  that  while  for  the 
low-frequency  three-phase  currents  the  action  remains  unaltered,  for 
the  high-frequency  current  the  motor  or  transformer  coils  are  non- 
inductive.  In  order  to  obtain  complete  control  over  the  high-frequency 
single-phase  E.M.F.,  the  inventors  use  a  stationary  armature,  in  whose 
core  are  embedded  the  conductors  of  the  three-phase  winding,  but  the 
fly-wheel  magnet  carries  a  double  set  of  pole-pieces,  one  corresponding 
to  the  low-frequency  three-phase  E.M.F.,  and  the  other — thrice  as 
numerous — ^giving  rise  to  the  single-phase  E.M.F.  of  thrice  the 
frequency.  The  advantages  of  low  frequency  for  power  work  and 
of  high  frequency  for  lighting  are  combined  in  this  folycyclic  system, 
as  it  is  termed  by  its  inventors.  A  considerable  saving  of  copper  is 
claimed  for  it,  in  addition  to  its  other  advantages. 

Mr.  M.  B.  Field  :    In  common  with  the  previous  speakers  I  attach    Mr.  Field, 
great  importance  to  the  subject  of  dielectric  hysteresis.     I  think  that  in 
all  probability  it  may  be  intimately  connected  with  the  breakdown 
voltage  an  insulating  material  will  stand.    What  I  mean  is  this :  H  one 


752  CONSTABLE  AND   FAWSSETT  [Mar.  26th' 

Mr.  Field.       takes  a  number  of  similar  slabs  of  a  given  dielectric  and  tests  them  up 

to  the  breakdown  point  it  would  probably  be  found  that,  other  things 

being  equal,  that  sample  will  break  down  first  which  has  the  greatest 

dielectric  loss,  and  I  would  go  further,  and  say  that  in  any  individual 

sample,  provided  the  electric  strain  is  uniform  over  the  surface,  it  will 

probably  break  down  at  that  spot  where  the  dielectric  loss  is  a  maximum. 

If  this  be  correct  it  gives  us  a  very  good  reason  for  examining  minutely 

this  question  of  dielectric  hysteresis  quite  apart  from  the  cost  of  the 

lost  power  thereby  engendered. 

Before  touching  on  that  point,  however,  I  would  like  to  call  attention 

to  the  fact  that  the  losses  to  which  Messrs.  Fawssett  and  Constable 

particularly  refer  are  not  wholly  confined  to  the  dielectric  ;  a  portion,  a 

very  small  portion  it's  true,  occurs  in  the  copper  itself,  so  that  a  cable  on 

open  circuit  which  is  insulated  with  a  perfect  dielectric  will  always  have 

a  power-factor  somewhat  greater  than  zero  due  to  the  CR  loss  in  the 

copper  core  which  the  charging  current  gives  rise  to.     If  C  be  the 

charging  current,  or  that  flowing  into  the  near  end  of  the  cable,  and  R 

is  the  total  resistance  of  the  **  go  and  return  "  conductors,  the  copper 

C*R 
loss  will  be .     The  apparent  power  is  V  C,  hence  the  power-factor 

is — 

CR 

or  writing  C  as  2  tt  «  K  V,  /?  being  the  frequency  and  K  the  total  capacity 
in  farads,  we  may  say  roughly  that — 

P.F.=  2«KR. 

This  shows  us  that  the  p.f.  is  proportional  to  the  square  of  the  length  of 
the  cable  and  to  the  frequency. 

Now  with  ordinary  lengths  of  cables  at  ordinary  frequencies  this 
power  factor  is  extremely  small,  e,g,  taking  lo  miles  of  No.  y  cable  we 
should  get — 

P.F.=  2  X  6o  X  8-36  X  8-8  X  10^  =  0088. 

This  of  course  is  a  very  small  pi.,  but  if  a  thirteenth  harmonic  were 
present  in  the  wave-form,  the  p.f.  relative  to  this  one  harmonic  would 
be  over  •!  i  or  practically  as  great  as  that  noted  for  Cable  7  in  Table  IV. 

The  above  rough  approximation  can  of  course  not  be  applied  for 
very  long  cables.  In  that  case  we  should  have  to  express  the  p.f.  in  the 
following  wav  : 

If  V  =  Vo  sin  k  t 
C  =  CoSin(*/  4-  n) 
at  the  near  end  of  the  cable,  then  17  may  be  split  up  into  three  compo- 
nents, ij  =  0  4-  e  4-  0,. 

The  values  of  ^  and  9  are  given  in  my  paper  on  page  689,  while  ^, 
is  such  that — 

.  „  ^           f'""^  sin  2  a  / 
tan  0,= , 

Now  if  we  assume  the  resistance  of  the  copper  is  vanishingly  small 
^  =5  0  and  0  +  0,  =    - ,  which  shows  us  that  in  this  case  only  can 


1903.] 


AND    FIELD:   DISCUSSION. 


763 


the  power  factor  be  zero.     Having  now  disposed  of  that  component  of  Mr.  Fidd. 
the  loss  which  occurs  in  the  copper  itself,  we  must  look  to  the  dielectric 
as  the  seat  of  the  greater  proportion  of  the  total  loss. 

It  is  very  striking  that  this  dielectric  loss  can  amount  to  more  than 
one-third  of  the  total  C'R  loss  in  the  H.T.  cables,  for  this  is  what 
Messrs.  Constable  and  Fawssett  tell  us. 

Towards  the  end  of  the  first  volume  of  Maxwell  the  case  of  a 
stratified  dielectric  is  mathematically  considered,  in  which  different 
values  of  conductivity  and  specific  inductive  capacity  are  assumed  for 
the  different  layers  and  the  phenomena  of  electric  absorption  and 
residual  discharge  are  explained  on  that  hypothesis.  We  then  find  the 
statement  that  the  same  reasoning  applies  and  similar  results  are 
obtained  if  instead  of  assuming  definite  strata,  we  consider  merely  a 
conglomeration  of  particles  with  different  constants  as  above.  This  is 
a  very  useful  conception  in  connection  with  many  manufacturers'  insul- 
ating materials.  Returning  to  the  simpler  conception  of  a  stratified 
dielectric  of  which  some  of  the  strata  act  more  or  less  as  slightly  conduct- 
ing layers  and  take  up  little  of  the  static  strain,  while  others  act  more 


Fig.  F. 

A  =  watts  generated  per  square  inch  of  surface  due  to  given 
voltage  at  given  frequency ;  B  B,  Ba  =  watts  dissipated  (with 
different  temperature  of  surroundings). 


truly  as  the  dielectric  medium  in  say  an  air  or  mica  condenser,  we  see 
that  we  could  consider  a  section  of  the  insulation  of  the  cable  say 
between  the  inner  and  outer  conductors  as  a  succession  of  capacities 
and  high  resistances  in  series.  Testing  such  a  combination  with  a  con- 
tinuous current,  it  is  clear  that  the  insulation  resistance  might  be  very 
high,  since  the  good  layers  would  take  up  the  static  strain.  Testing 
with  an  alternating  current,  however,  one  might  find  considerable  loss 
and  heating  owing  to  the  capacity  currents  flowing  through  the 
bad  or  semi-conducting  layers. 

In  this  case  the  loss  would  be  proportional  to  the  square  of  the 
voltage  and  to  the  square  of  the  frequency,  while  the  power-factor 
would  be  proportional  to  the  frequency. 

I  notice  in  Table  V.  the  approxinjate  Ipss  in  a  paper  cable  is  shown  ? 


754  CONSTABLE   AND   FAWSSETT  [Mar.  26th, 

.  Field.      proportional  to  the  square  of  the  voltage,  and  I  would  like  to  ask  how 
this  table  was  derived,  whether  it  rests  on  experiment  or  theory. 

I  said  just  now  that  it  was  probable  the  "  breakdown  "  strength  of  an 
insulating  material  was  closely  related  to  the  dielectric  loss,  and  I 
would  like  to  explain  what  I  mean. 

If  we  place  a  uniform  slab  of  some  dielectric  compound  between  two 
.netal  plates  so  as  to  form  a  condenser,  apply  an  alternating  voltage,  and 
measure  the  loss  per  unit  area  of  surface  at  different  temperatures 
of  the  dielectric,  we  find  that  after  a  certain  temperature  is  reached,  the 
loss  increases  at  a  very  rapid  rate.  Now  the  rate  at  which  the  heat  can 
get  away  from  the  slab  naturally  depends  on  a  large  number  of  circum- 
stances, but  principally  upon  the  difference  of  temperature  between  the 
slab  itself  and  the  surroundings.  Superimposing  the  two  curves  of 
watts  generated  (due  to  a  given  alternating  voltage  at  given  frequency) 
and  watts  which  can  be  dissipated  (by  conduction,  radiation,  etc)  per 
square  cm.  of  surface,  we  get  curves  such  as  A  and  B  in  the  figure 
above.  At  the  temperature  /,  the  heat  generated  is  greater  than  that 
got  rid  of,  so  the  temperature  of  the  material  would  tend  to  rise.  At 
the  temperature  4»  on  the  other  hand,  the  energy  which  the  slab  can  get 
rid  of  per  second  is  greater  than  that  generated,  hence  there  will  be  a 
tendency  for  the  material  to  fall.  T  will  therefore  be  a  temperature 
at  which  the  material  will  eventually  arrive,  since  at  this  temperature 
the  rate  of  generation  of  heat  is  equal  to  the  rate  of  dissipation. 
Should  however  the  temperature  of  the  slab  by  any  means  rise  above 
T„  it  might  be  said  to  be  in  an  unstable  state,  for  the  temperature  would 
then  continually  increase  until  the  insulating  properties  of  the  material 
were  destroyed  by  charring.  The  effect  of  increasing  the  temperature 
of  the  surroundings  will  be  to  materially  raise  the  final  temperature  T 
to  which  the  material  will  rise,  for  in  this  case  the  curve  representing 
watts  dissipated  will  be  B,  instead  of  B.  Again,  if  we  increase  the 
surrounding  temperature  still  further,  we  find  that  there  will  be  no  final 
temperature  at  all,  but  that  the  slab  will  get  hotter  and  hotter  until  it 
chars.  If  now  there  is  a  spot  in  the  slab  which  is  weaker  than  else- 
where, more  heat  per  unit  area  will  be  generated  here,  and  the  temper- 
ature will  rise  locally  at  this  point.  In  fact,  it  seems  possible  for  the 
temperature  to  rise  at  a  weak  spot  to  such  a  limit  that  actual  scorching 
occurs  there  without  the  rest  of  the  material  being  damaged.  As  soon 
as  this  occurs  the  insulation  breaks  down,  an  arc  follows,  and  in  all 
probability  destroys  all  traces  of  the  gradual  burning  which  has  pre- 
ceded. In  corroboration  of  this  theory,  which  was  verbally  explained 
to  me  by  Mr.  Miles  Walker  after  he  had  conducted  a  number  of  experi- 
ments in  this  direction,  I  would  instance  the  following  facts. 

ist.  The  voltage  that  many  materials,  such  as  paper,  prepared  linen, 
prcsspahn,  etc,  will  stand  depends  in  some  way  inversely  as  the  time 
of  application.  For  example,  a  layer  of  paper  will  often  withstand 
15,000  volts  for  an  instant,  when  it  will  not  stand  5,000  continuously. 

2nd.  If  slabs  be  tested  as  above  described,  and  the  voltage  be  applied 
for  gradually  increasing  periods  of  time,  and  if  they  are  examined  after 
each  application,  it  will  often  be  found  that  scorching  has  occurred  at 
some  point  without  actually  brea  ing  down,  and  if  the  material  be 


1903.]  AND   FIELD:   DISCUSSION.  755 

again  tested  under  electric  pressure  it  will  finally  break  down  at  this   Mr.  Field, 
point. 

3rd.  In  testing  insulating  tubes,  etc.,  it  is  quite  a  usual  practice  to 
put  a  number  under  a  high  voltage  test  for  a  few  minutes  and  then  to 
feel  them.  The  hot  ones  are  cast  aside  as  bad,  since  it  has  been  found 
by  experience  that  these  would  in  the  long  run  give  out. 

4th.  Those  materials  which  do  not  change  their  composition  when 
subjected  to  a  high  temperature  are  usually  found  to  be  the  best  insula- 
lators,  e.g.,  mica,  porcelain,  glass,  ambroin,  and  even  air.  Should  the 
above  theory  be  correct,  we  see  that  it  will  lead  us  to  the  important 
conclusion  that  the  breakdown  strength  depends  also  on  the  frequency, 
and  a  material  which  easily  burns  would  be  much  stronger  if  tested 
with  continuous  voltage  than  with  an  alternating.  We  further  see  that 
inflammable  materials  will  have  two  strengths  entirely  different,  one  in 
withstanding  mechanical  piercing  due  to  a  strain  of  very  short  duration 
where  the  heating  effect  cannot  come  into  play,  and  the  other  in  with- 
standing prolonged  strains.  It  seems  probable  that  air  and  certain 
other  insulators  only  break  down  through  piercing,  i.e.,  in  the  first-men- 
tioned manner. 

To  my  mind  a  careful  investigation  into  this  whole  matter  would  be 
of  the  greatest  practical  importance  to  the  designers  of  electrical 
machinery. 

Mr.  W.  M.  MoRDEY  :  Mr.  Constable  and  Mr.  Fawssett  deal  with  the  Mr. 
distribution  losses  in  the  very  practical  form  of  a  detailed  examination  Mordey. 
of  the  actual  losses  in  the  Croydon  system.  Although  we  have  at  this 
Institution  often  discussed  the  subject  of  lost  units,  I  do  not  think  it  has 
ever  been  put  before  us  in  so  telling  and  complete  a  way.  It  is  saddening 
to  think  that  after  all  the  efforts  of  the  last  twenty  years  the  losses  in  a 
well-considered  distribution  system  should  be  22  per  cent,  of  the  energy 
sent  out  of  the  generating  station. 

Such  a  paper  shows  clearly  the  direction  in  which  we  must  work  if 
we  desire  to  reduce  the  distribution  losses.  Some  of  the  losses  can 
only  be  reduced  by  an  outlay  which  would  be  unsound  commercially, 
but  some  may  perhaps  be  lessened. 

The  authors  treat  only  of  distribution  losses.  When  they  have 
exhausted  that  subject  they  may  turn  their  attention  to  the  inside  of 
the  station,  when  they  will  find  there  is  a  loss  of  coal  of  about  50  per  cent, 
which,  on  paper  at  any  rate,  is  capable  of  being  saved.  Then  they  may 
study  the  loss  of  about  85  per  cent,  in  converting  the  heat  energy  of  the 
coal  into  mechanical  energy  in  the  boiler  and  engine  ;  and  when  they 
have  studied  those  few  small  losses  they  may  continue  their  investiga- 
tions and  consider  the  loss  of  more  than  99  per  cent,  in  the  incandescent 
lamp  itself  between  the  heat  energy  given  to  the  lamp  and  the  light 
energy  given  out. 

You  will  find,  sir,  that  we  shall  not  exhaust  this  subject  to-night ! 

Before  going  on  to  the  matter  that  interests  me  a  good  deal,  that  of 
the  losses  in  the  dielectric,  I  would  like  to  refer  to  the  question  of 
switching  transformers  off,  mentioned  by  the  authors  at  page  723. 
It  is  generally  believed  that  for  economical  working  it  is  necessary 
to    keep    transformers    as    nearly  fully  loaded    as    possible — this    is 


756  CONSTABLE  AND   FAWSSETT  [Mar.  26th, 

Mr.  not    by    any    means    the    case.    There    is    often    no    advantage    in 

*^*  switching  transformers  off;  there  may  even  be  a  disadvantage  in 
doing  so.  The  efficiency  curve  of  a  good  transformer  is  square- 
shouldered  ;  it  goes  up  quickly,  to  practically  full  efficiency,  and  then 
keeps  nearly  straight  up  to  full  load,  often  indeed  falling  a  little  as  full 
load  approaches.  Now  with  such  conditions  two  half-loaded  trans- 
formers are  as  efficient  as  one  fully  loaded  ;  if  the  curve  drops  a  little, 
the  two  will  be  even  more  efficient. 

For  transformers  having  efficiency  curves  which  reach  practically 
full  value  at  one-third  load,  three  of  them,  each  one-third  loaded,  will 
be  as  efficient  as  one  fully  loaded.  Under  such  conditions  it  is  best  not 
to  keep  transformers  fully  loaded  ;  it  does  not  save  energy,  and  it  is 
bad  for  the  transformers.  If  a  given  amount  of  energy  is  to  be  wasted, 
it  is  better  to  spread  it  over  a  number  of  transformers  than  to  concen- 
trate it  in  one — better  for  the  transformers,  and  it  lowers  the  copper  loss. 

Turning  now  to  the  question  of  losses  in  the  dielectric  of  the  cable, 
I  quite  agree  with  the  authors  in  disliking  the  term.  If  the  last  speaker 
— who  seems  to  have  a  liking  for  correctness  in  terms — could  invent 
some  term  which  is  less  cumbrous  and  more  like  Anglo-Saxon  than 
"dielectric  hysteresis,"  we  should  all  be  very  grateful  to  him. 

The  paper  that  I  read  here  some  time  ago  on  that  subject  has  been 
referred  to  by  the  authors  and  by  one  or  two  speakers.  I  was  rather 
badly  treated  in  that  discussion ;  it  was  apparently  felt  that  in  sug- 
gesting we  had  overlooked  a  serious  cause  of  loss  of  energy,  I  had 
committed  a  crime  of  the  most  heinous  character  !  But  time  brings 
its  revenges.  As  the  authors  say,  the  subject  was  not  exhausted  then, 
and  I  am  very  glad  indeed  they  have  contributed  to  its  further  elucida- 
tion. There  is  a  good  deal  to  be  done  before  we  have  got  to  the  bottom 
of  that  subject.  But  it  is  one  that  we  must  consider.  If  there  is  a 
possibility  of  power-factors  of  anything  like  the  order  I  mentioned  in 
my  paper — now  confirmed  by  the  present  authors— or,  I  will  go  further 
and  say  that  if  there  are  power-factors  of  a  much  lower  order — such  as 
Mr.  Duddell  says  he  is  satisfied  do  commonly  exist — it  is  a  matter  of 
real  engineering  importance,  especially  for  long  distance  high-pressure 
work.  We  must  try  and  find  some  simple  way  of  measuring  these 
losses.  The  authors  and  Mr.  Duddell — ^an  investigator  who  should  be 
carefully  cherished — have  used  certain  methods  which  are  probably 
the  best  now  available,  but  we  want  something  more  direct.  I  would 
suggest  calorimetric  methods.  Direct  measurement  of  the  rise  of  tem- 
perature is  of  course  hardly  practicable.  Under  ordinary  conditions 
even  a  serious  loss  of  energy  would  not  cause  any  noticeable  rise  of 
temperature  in  a  cable. 

It  ought,  however,  to  be  possible  to  put  a  cable  into  a  heat- 
insulated  bath  of  oil  or  water  and  to  run  it  and  observe  the  rise 
of  temperature  that  takes  place  when  it  is  subject  to  high  electro- 
motive forces.  It  should  then  be  possible  to  get  the  same  rise 
and  therefore  the  same  loss  by  sending  a  direct  current  through 
the  conductor  of  the  cable  and  so  measure  the  direct  current  energy 
easily.  I  do  not  say  there  are  no  difficulties.  To  what  extent  the 
losses  are  eddy-current  losses  is  a  matter  to  which  attention   must 


1903.]  AND   FIELD:  DISCUSSION.  757 

be  given.     But  I  think  there  are  ways  of  making  calorimetric  test.s  Mr. 


under  conditions  where,  if  eddy-current  losses  exist,  they  may  be  kfept 
so  small  as  to  be  negligible,  or,  in  any  case,  their  amount  can  be 
measured.  This  latter  might  be  done  by  determining  the  loss,  other  than 
that  due  to  resistance  and  current,  by  sending  a  low-tension  alternate 
current  through  a  cable  in  the  calorimeter;  under  these  conditions 
there  would  be  no  dielectric  loss. 

When  I  read  a  paper  on  Capacity  Effects  before  this  Institution,  the 
discussion  was  associated  with  a  good  deal  of  heat  other  than  what  is 
usually  measured  by  a  thermometer.  I  hope  we  shall  now  discuss  it 
calmly  and  find  out  seriously  whether  it  is  a  loss  which  engineers- 
makers  or  users  of  cables — need  consider.  It  is  far  more  important  to 
be  sure  that  there  is  a  small  dielectric  loss  than  that  the  copper  has  a 
high  conductivity.  If  it  is  necessary  to  specify  the  latter  carefully, 
much  more  important  is  it  to  consider  a  cause  of  loss  which  may  be 
hundreds  of  times  gre^lter  than  that  caused  by  the  copper  being  0*96 
instead  of  0*98  of  Matthiessen's  standard  of  conductivity. 

May  I  be  allowed  to  give  as  an  example  a  few  figures  to  show  that 
this  matter  is  of  real  importance  even  with  small  power-factors  ?    It  is 
not  denied,  I  think,  that  there  may  be  such  power-factors  as  o'l,  but  let 
us  take  the  lower  values  of  0*025  or  0*03  which  Mr.  Duddell's  experi- 
ments lead  him  to  say  need  not  be  exceeded  in  any  good  cable.     I  do 
not,  however,  agree  with  him  that  with  such  values  the  matter  is  of  no 
importance ;  even  a  o'oi  power-factor  may  be  of  importance.    Let  us 
take  a  case  which  may  easily  occur  in  practice.    Assume  a  10,000-volt 
three-phase  cable  for  a  transmission  system  supplying  such  an  area  as 
many  power  schemes  are  now  proposing  to  deal  with.    Assume  it  has  a 
capacity  of  0*3  microfarad  per  mile,  and  a  power-factor  of  0*03 — then 
the  loss  would  be  7,400  units  a  year  for  every  mile  of  cable,  or  about 
equal  to  an  8-c.p.  lamp,  always  alight,  for  every  63  yards  of  cable. 
Assume  this  cable  is  ten  miles  long  and  is  supplying  a  small  town 
having  an  ordinary  12  per  cent,  load-factor  and  a  **  maximum  demand  " 
of  300  kw. — the  ordinary  "  authorised  distributor  "  of  the  power  bills — 
then  the  dielectric  loss  in  the  cable  will  be  23*4  per  cent,  of  the  energy 
delivered,  or  as  much  (in  percentage)  as  the  authors  show  is  lost  in  the 
whole  system  at  Croydon  in  transmission  and  distribution. 
If  this  is  true,  the  question  deserves  serious  attention. 
It  would  be  interesting — in  these  days  of  power  bills  and  long- 
distance high-pressure  schemes — to  follow  this  point  a  little  further, 
but  I  will  only  point  out  that  if  the  copper  loss  in  this  cable  is  5  per 
cent,  and  if  the  **  authorised  distributor "  loses  only  20  per  cent,  in 
distribution,  then  the  generating  station  must  send  into  that  cable  about 
48*5  per  cent,  more  energy  than  ever  reaches  the  customers.  One  point, 
however,  must  not  be  lost  sight  of  :  the  dielectric  loss,  whatever  it  may 
be,  does  not  greatly  increase  with  the  size  of  the  cable  ;  thus  it  will  be 
relatively  less  serious  on  a  cable  for  a  large  load  than  for  a  small  one. 
For  the  latter  it  may  be  serious  enough  to  prevent  the  economical 
supply  of  small  towns  through   long  underground  cables,  and   may 
strongly  support  the  demand  for  bare  overhead  conductors. 

One  other  point— this  loss  is  not  a  capacity  loss  at  all,  but  a  kind  of 


MorJey. 


758 


ELECTIONS. 


[Mar.  26th, 


Mr. 

Mordcy. 


resistance  loss  having  a  unity  power-factor  of  its  own  ;  it  would  take 
place  just  the  same  if  the  cable  had  no  evident  capacity. 

The  President  announced  that  the  scrutineers  reported  the  follow- 
ing candidates  to  have  been  duly  elected  : — 


Ovide  F.  Domon. 


Members, 

I       Giovanni  Giorgi. 
Wyndham  Monson  Madden. 


Associate  Members. 


Frank  Anslow. 
Robert  Malcolm  Campbell. 
Johan  Denis  Carlmark. 
John  Mathieson  Kcenan. 


Walter  Henry  Le  Grand. 
John  F.  Magoris. 
John  Frederick  Pierce. 
Theodore  Rich. 


Harold  Stokes. 


Associates, 


Arthur  Chester. 
Edward  Alan  Christian. 
Wm.  Frederick  Coakcr . 
Wm.  Thomas  Dalton. 
Theodore  J.  Valentine  Feilden. 
Thos.  Henry  Flam  well. 


John  Walker  Fyfe. 
Chas.  Ward  Hammertoa 
Hugh  Henry  McLeod. 
Chas.  Edward  Harrison  Perkins. 
Louis  Boniface  Wilmot. 
Clifford  George  Woodley. 


Students, 


Herbet  Paul  Amphlett. 
William  Bell  Begg. 
Eric  Frank  Cliff. 
William  Prescott  Crooke. 
Thomas  Davies. 
Henry  T.  Debcnham. 
Eustace  Jonathan  Down. 
Henry  Firth. 


Martin  Julius  Wolff. 


Charles  Butter  Grace. 
Harry  LilPwhite. 
Joseph  F.  Mongiardino. 
Leonard  John  Pumphrey. 
Chas.  Alexander  Rainsford. 
Roy  Grosvenor  Thomas. 
Geo.  Keenlyside  Tweedy. 
James  L.  Wilson. 


1903.]         TRANSFERS,   DONATIONS  TO   LIBRARY,   ETC.  769 


The  Three  Hundred  and  Ninety-second  Ordinary  General 
Meeting  of  the  Institution  was  held  at  the  Institution 
of  Civil  Engineers,  Great  George  Street,  Westminster, 
on  Thursday  evening,  April  23,  1903 — Mr.  Robert  K. 
Gray,  President,  in  the  Chair. 

The  minutes  of  the  Ordinary  General  Meeting  held  on  March  26th, 
1903,  were  taken  as  read  and  signed  by  the  President. 

The  names  of   candidates  for  election   into  the   Institution   were 
taken  as  read,  and  ordered  to  be  suspended  in  the  usual  form. 

The  following  list  of  transfers  was  published  as  having  been  approved 
by  the  Council  — 

From  the  class  of  Associates  to  that  of  Members— 

Walter  Joseph  Higley. 

From  the  class  of  Foreign  Members  to  that  of  Members^ — 

Frederico  Pescetto. 

From  the  class  of  Associates  to  that  of  Associate  Members — 

Frederic  Robert  Bridger.  I       William  Richard  Kelsey. 

Robert  Marshall  Carr.  I       Theodore  Arnold  Locke. 

Robert  Tyndall  Haws.  j       Arnold  Philip. 

Francis  C.  Hounsfield.  |       Maurice  Solomon. 

T.  B.  Wright. 

From  the  class  of  Students  to  that  of  Associate  Members — 
Frederic  Chas.  Kidman.  |  John  Warrack. 

From  the  class  of  Student  to  that  of  Associate — 
Arthur  John  Cridge.  |  Alfred  Eddington. 

Messrs.  H.  Brazil  and  L.  T.  Healey  were  appointed  scrutineers  of 
the  ballot  for  the  election  of  new  members. 

Donations  to  the  Library  were  announced  as  having  been  received 
since  the  last  meeting  from  Messrs.  A.  Hcyland,  H.  A.  Humphrey, 
E.  and  F.  N.  Spon  ;  to  the  Building  Fund  from  Messrs.  B.  G.  Jones, 
H.  T.  Lines,  A.  Nield ;  and  to  the  Benevolent  Fund  by  Mr.  S.  E.  Britton, 
to  whom  the  thanks  of  the  meeting  were  duly  accorded. 
Vol.  82.  60 


760 


MEMBERS  NOMINATED  BY  THE   COUNCIL    [April  28rd, 


The  Secretary  read  the  following  nominations  by  the  Council  for  the 
officers  and  Council  for  the  ensuing  Session  ; — 

MEMBERS  NOMINATED    BY  THE    COUNCIL    FOR    OFFICE 

1903-1904. 


Nomination, 

Remaining  in  Office, 
New  Nominations, 


As  President, 
Robert  Kaye  Gray. 

As  Vice-Presidents  (4). 

(John  Gavey. 
(Sir  Oliver  Lodge,  F.R.S. 
( Dr.  J.  A.  Fleming,  F.R.S. 
Ij.  E.  Kingsbury. 


Remaining  in  Office, 


New  Nominations, 


Ordinary  Members  of  Council  (15). 

/Sir  John  Wolfe  Barry,  K.C.B.,  F.R.S. 

S.  DOBSON. 

Bernard  Drake. 
H.  E.  Harrison. 

1Lt.-Col.  H.  C.  L.  Holden,  R.A.,  F.R.S. 
The  Hon.  C.  A.  Parsons,  F.R.S. 
W.  H.  Patchell. 
J.  H.  Rider. 
A.  A.  Campbell  Swinton. 
/T.  O.  Callendar. 
S.  Z.  DE  Ferranti. 
Frank  Gill. 

F.  E.  Gripper. 

G.  Marconi. 
W.  M.  Mordey. 


As  Associate  Members  of  Council  (3). 


Remaining  in  Office, 
New  Nomination, 


For  Re-Election, 


For  Re-Election, 


For  Re-Election. 


(W.  DUDDELL. 

(Sydney  Morse. 
A.  J.  Walter. 

As  Honorary  Auditors, 

( F.  C.  Danvers. 
(Sidney  Sharp. 

As  Honorary  Treasurer, 
Robert  Hammond. 

As  Honorary  Solicitors, 
Messrs.  Wilson,  Bristows  &  Carpmael* 


1903.]  FOR   OFFICE   1903-1904.  761 

The  President  :  Before  the  discussion  of  the  papers  of  Mr.  Field 
and  Messrs.  Constable  and  Fawssett  is  op^ened,  I  desire  to  ma^e  a  few 
remarks  with  regard  to  the  recent  visit  to  the  North  of  Italy  of  about 
I20  members  of  the  Institution.  The  object  of  these  remarks  is  to 
place  on  record,  in  the  Proceedings  of  the  first  meeting  held  "since  our 
return,  the  sense  of  gratitude  felt  by  the  Institution  for  the  great 
kindness  shown  by  our  Italian  hosts. 

In  addition  to  the  many  interesting  visits  which  had  been  arranged, 
the  very  cordial  reception  given  to  the  party  was  quite  remarkable. 
Senator  Colombo,  who  had  been  in  Rome,  made  a  point  of  coming  to 
Milan  to  meet  us.  Professor  Ascoli,  the  President  of  the  Associazione 
Elettrotecnica  Italiana,  also  came  from  Rome  to  preside  at  the  banquet 
given  in  our  honour  by  that  body.  Mr.  Blathy,  of  Messrs.  Ganz  and 
Co.,  came  specially  from  Buda-Pest  to  assist  in  showing  us  the  Valtellina 
line,  in  the  electrification  of  which  his  firm  played  a  preponderant  role, 
Mr.  Cini,  of  the  Adriatic  Railway  Company,  who  are  interested  in  the 
Valtellina  line,  came  from  Florence.  Our  visit  to  the  Tornavento  Power 
Station,  with  the  inspection  of  the  electrified  Milan- Varese  line,  was 
rendered  more  instructive  and  agreeable  by  the  presence  of  Mr.  Kossuth, 
one  of  the  Directors  of  the  Mediterranean  Railway  Company,  and  of 
Monsieur  Lagout,  of  the  Thomson- Houston  Company  de  la  Mediter- 
ranee,  who  came  from  Paris  with  the  object  of  accompanying  us  and 
showing  us  the  work  of  his  firm.  Senator  Colombo  and  his  friends 
showed  us  the  large  water-power  station,  at  Paderno,  of  the  Italian 
Edison  Company,  and  also  their  Distributing  Stations  in  Milan.  Senator 
De-Angeli  conducted  us  to  the  Vizzola  Water-Power  Station  of  the 
Societa  Lombarda  per  Distribuzione  di  Energia  Elettrica.  In  addition 
to  these,  the  Chairman  of  the  Milan  section  of  the  Associazione  Italiana 
Elettrotecnica,  Mr.  Bertini,  and  the  Secretary — Mr.  Semenza — had, 
through  the  courtesy  of  the  proprietors,  enabled  us  to  visit  several 
works  in  the  neighbourhood  of  Milan  and  in  Milan  itself  which  proved 
of  great  interest  to  the  visitors.  It  is  impossible  to  thank  Mr.  Semenza 
too  much  for  the  enormous  labour  he  must  have  gone  through  to 
provide  for  the  entertainment  of  a  numerous  body.  The  Council  will  in 
due  course  tender  the  thanks  of  the  Institution  to  our  late  hosts  in  a 
more  formal  manner. 

Before  terminating  I  think  I  should  inform  the  members  of  the 
Institution  that  the  visit  to  the  North  of  Italy  is  considered  by  all  who 
took  part  in  it  as  a  very  successful  one,  and  that  Dr.  Silvanus  Thompson, 
who  had  taken  so  much  trouble  in  initiating  it,  Mr.  Hammond,  the 
reporter  of  the  Foreign  Visits  Committee,  and  our  Secretary — Mr. 
McMillan — who  so  successfully  carried  out  all  the  details  of  the  expedi- 
tion, certainly  earned  the  praise  which  they  received  from  all  sides. 

With  these  remarks  I  shall  now  call  upon  Professor  Carus- Wilson  to 
open  the  adjourned  discussion  on  the  papers  read  by  Mr.  Field  and 
by  Messrs.  Constable  and  Fawssett. 


762  CONSTABLE  AND   PAWSSETT  [April  23ni, 

Resumed  Discussion  on  Papers  on  **  Distribution  Laws  in  Elec- 
Tinc  Supply  S\'stems,"  by  A.  D.  Constable,  A.M.LE.E.,  and  E. 
Fawssett,  A.LE.E.,  and  "A  Study  of  the  Phenomenon  of 
Resonance  in  Electric  Circuits  by  the  aid  of  Oscillograms," 
BY  M.  B.  Field,  M.LE.E.,  A.M.LC.E. 

Pro^  Caru8-  Professor  C.  A.  Carus- Wilson  :  Mr.  Field  has  brought  before  us  a 
subject  of  great  importance  and  interest,  and  has  illustrated  his  paper 
by  showing  us  some  interesting  slides.  Mr.  Duddell  has  supplemented 
what  Mr.  Field  has  given  us  by  further  illustrations  of  resonance  in 
transmission  circuits,  and  the  jagged,  saw-like  curves  which  he  showed 
were  calculated  to  alarm  us,  especially  when  accompanied  by  statements 
that  they  involved  very  high  voltage.  The  question  I  want  to  raise 
to-night  is  whether  the  effects  that  have  been  shown  to  us  are  really 
serious,  in  view  of  the  actual  strains  to  which  high-tension  circuits  are 
subject  in  every-day  working.  Mr.  Field  in  his  paper  rightly  alludes  to 
what  has  been  written  on  this  subject  in  the  United  States,  and  draws 
attention  to  the  communications  that  from  time  to  time  have  appeared 
on  this  subject  in  the  transactions  of  the  American  Institute  of  Elec- 
trical Engineers.  I  quite  agree  with  him  in  thinking  that  those  transac- 
tions are  not  as  well  read  on  this  side  as  they  should  be,  and  I  am  also 
surprised  that  more  members  of  our  own  Institution  are  not  members 
of  the  American  Institution.  I  notice,  however,  that  his  paper  gives 
us  several  results  which  have  already  been  arrived  at  by  other  workers. 
For  instance,  the  equations  he  gives  us  at  the  bottom  of  p.  685,  for  the 
induced  pressure  due  to  sudden  and  rapid  oscillating  effects  consequent 
upon  breaking  a  circuit  with  a  load  on,  are  the  same  as  those  given  by 
Mr.  Steinmetz  two  years  ago,  though  arrived  at  by  a  different  process. 
On  p.  691  the  equations  that  Mr.  Field  gets  for  the  rise  of  pressure,  due 
to  resonance,  at  the  end  of  the  long  transmission  line,  appear  to  me  to  be 
identical  in  result,  with  some  slight  exceptions,  to  which  I  will  refer 
later,  with  those  given  by  Houston  and  Kennelly  in  1895.  I  refer  to 
these  facts  simply  to  point  out  that  Mr.  Field  has  arrived  at  the  same 
results  by  working  out  these  problems  on  independent  lines  from  his  own 
standpoint,  in  a  way  quite  different  from  what  others  have  done.  On 
p.  691  Mr.  Field  gives  the  fundamental  conditions  for  resonance,  and  an 
equation  for  the  rise  of  voltage  at  the  end  of  a  long  transmission  Une. 
I  do  not  see  why  he  needs  such  a  confusion  of  terms  at  the  bottom  of 
p.  688,  where  he  introduces  Greek  letters  as  well  as  Roman  letters ;  1 
have  not  quite  been  able  to  follow  him  in  that.  Surely  it  is  simpler  to 
express  the  condition  of  maximum  resonance  by  the  expression — 


In  the  way  Mr.  Field  gives  it  we  have  to  look  back  to  a  complicated 
series  of  equations  in  order  to  understand  it.  [Communicated,  After 
hearing  Mr.  Field's  explanation  of  his  symbols  I  admit  that  his  equa- 
tions are  quite  as  simple  as  the  one  I  have  given  above.]  I  should  like 
to  show  on  the  blackboard  what  this  distance  /  really  is.  If  A  is  the 
receiving  end  and  H  the  sending  end,  then  the  pressure  is  a  maximum 


1903.] 


AND   FIELD:   DISCUSSION. 


763 


of  V,  volts  at  A,  and  as  we  get  nearer  the  sending  end  the  pressure 
drops  to  a  minimum  of  Vo  volts,  and  rises  again  if  the  line  is  long 
enough.  The  length  /  between  the  positions  of  maximum  and  minimum 
pressure  is  given  by  the  above  equation.  In  practice  this  distance  is  very 


Prof.  Canis- 
Wilson. 


Fig.  G. 


great.  In  a  case  which  I  had  occasion  to  work  out  recently  for  a  three- 
phase  transmission  line  about  loo  miles  in  length,  this  distance  came 
out  to  1,430  miles,  that  is  to  say,  in  order  to  get  the  maximum  resonance 
effect  the  line  would  have  to  be  1,430  miles  long,  whereas  the  line  was 
only  100  miles  long.  Consequently  the  actual  rise  of  voltage  due  to 
resonance  was  a  mere  nothing.  In  the  next  equation  Mr.  Field  gives  us 
an  expression  for  the  relation  between  Vo  and  V„  from  which  we  can 
find  the  rise  of  pressure  due  to  resonance.  I  cannot  help  thinking  that 
Mr.  Field  or  his  printer  has  made  a  slip  in  that  equation  ;  he  has  in  the 
denominator — 


I  think  that  should  be — 


—  2  t'~  *  ^''*"  *^ 


-f-   2  t'~  ftantf 


for  then  that  rather  complicated  equation  becomes  simply — 
V« 


V, 


=  cosh  /  a 


That  is  the  usual  form  of  the  expression  for  this  ratio,  where  /  is  the 
length  in  miles  and  a  is  the  quantity  depending  on  r,  \,  and  ;}. 

In  the  case  of  the  long  transmission  line  to  which  I  referred,  taking 
L  at  100  miles,  the  total  rise  in  voltage  did  not  amount  to  more  than 
2  per  cent.,  that  is  to  say,  not  only  is  the  line  required  to  get  the  maxi- 
mum resonance  effect  of  great  length,  far  beyond  anything  that  we  get 
in  practice,  but  the  actual  rise  is  quite  insignificant.  I  think  it  is  now 
generally  recognised  that  resonance  effects  in  long  distance  trans- 
missions are  really  of  no  importance.  When  we  get  the  frequencies  of 
the  higher  harmonics  that  Mr.  Field's  paper  deals  with,  we  get  r^son- 


764  CONSTABLE   AND   FAWSSETT  [April  23rd, 

Prof.  can».   ance  effects,  but  they  are  so  small,  on  account  of  the  very  small  ampli- 
tude of  the  waves  that  are  magnified,  that  the  increase  in  pressure  above 
the  normal  voltage  is  a  very  small  percentage  when  you  compare  peak 
with  peak  or  mean  with  mean.    I  take  it,  then,  that  in  actual  practice 
these  resonant  effects  are  extremely  small  in  long-distance  transmissions, 
even  when  you  take  account  of  the  higher  harmonics.    But  not  only 
that,  the  effects  of  resonance,  to  which  allusion  has  been  made  by  Mr. 
Field  and  Mr.  Duddell,  are  altogether  insignificant  when  you  come  to 
consider  the  strains  that  are  actually  put  upon  high-tension  transmission 
apparatus  by  oscillating  discharges.    I  notice  that  Mr.  Field  refers  to 
all  the  effects  dealt  with  in  his  paper  as  resonance  effects.     I  have 
always  understood  that  the  term  resonance  referred  to  a  stationary  wave, 
the  kind  of  thing  shown  in  the  diagram,  which  is  a  permanent  condition 
of  affairs.    That  was  the  meaning  of  the  term  adopted  by  the  people 
who  introduced  the  expression  ;  but  in  this  paper,  and  in  other  places 
also,  resonance  has  come  to  be  applied  to  a  great  many  other  effects 
accompanying  high  tension ;  for  instance,  oscillatory  effects.     I  quite 
think  that  those  are  the  phenomena  we  have  to  fear  in  a  transmission 
circuit,  but  they  are  not  resonance  effects  at  all,  since  they  are  not  due 
to  stationary  waves — they  are  due  entirely  to  momentary  changes  in  the 
conditions  of  loading  the  line.    These  arc  the  really  important  effects  to 
be  considered,  since  they  subject  transmission  lines  to  enormous  ten- 
sions, far  greater  than  any  due  to  resonance.     It  would  be  a  good  thing 
if  we  could  get  some  more  tests  made  on  these  oscillatory  effects.    The 
equation  for  V  on  page  685  of  Mr.  Field's  paper  gives  the  pressure 
caused   by  suddenly  breaking  a  circuit  with  a  load  on.    The  term 

f  V,*  -f-  C 1^  J  indicates  the  degree  of  strain  that  is  put  upon  the 

insulating  material,  from  which  it  appears  that  the  strain  upon  the  insula- 
ting apparatus  depends  upon  the  load,  and  is  proportional  to  the  current 
that  is  being   broken,  and  that  if  the  circuit  could  be  broken  when 
C  =:  O  there  would  be  no  rise  of  pressure.  This  is  entirely  borne  out  by 
tests  made  on  some  long-distance  transmission  lines  in  the  United  States, 
when  it  was  found  that  the  high  voltage  induced  by  breaking  the  circuit 
was  entirely  a  question  of  the  load  that  happened  to  be  on  the  circuit  at 
the  instant  of  the  break.    When  the  load  was  broken  under  oil,  the 
effect  of  the  break,  as  shown  by  means  of  an  oscillograph,  was  like  this : — 
There  is  an  oscillating  discharge  extending  for  a 
few  waves,  and  then  the  oil  breaks  the  circuit  at 
the  zero  point.  'If  it  were  not  for  the  fact  that 
an  oil  switch  breaks  the  circuit  at  zero  point,  I 
think  it  would  not  be  too  much  to  say  that  high- 
tension  long-distance  transmissions  carrying  very 
large  currents  would  be  impossible.      But  it  is 
Fig.  H.  found  in  practice  that  the  effect  of  oil  is  to  allow 

the  arc  to  spring  just  for  a  short  time,  extending 
over  about  half  a  dozen  waves,  and  then  to  break  the  circuit  at  the 
zero  point,  that  is  to  say,  in  a  remarkable  way  the  oil  switch  does 
exactly  what  we  should  want  it  to  do,  and  breaks  the  circuit  at  the 
moment  when  the  current  is  nothing,  thereby  enabling  the  circuit  to  be 


yo 


1908.]  AND   FIELD:  DISCUSSION.  766 

broken  without  any  rise  of  pressure.  In  the  tests  I  referred  to,  currents  Prof,  carus- 
of  30  amperes  at  40,000  volts  were  broken  by  an  oil  switch  without  any  *°°* 
rise  in  the  voltage  being  shown  on  the  oscillograph.  The  danger  of 
breaking  a  high-tension  circuit  may  thus  be  less  than  that  of  making 
the  circuit,  for  I  do  not  know  of  any  switch  by  which  the  high  voltage 
that  you  get  when  making  a  transmission  circuit  can  be  prevented, 
unless,  of  course,  rheostats  are  used.  It  would  appear,  then,  that 
transmission  circuits  may  be  subject  in  ordinary  working  to  very  high 
pressures  due  to  oscillatory  discharges  altogether  out  of  proportion  to 
the  effects  due  to  resonance,  twice,  or  even  three  times,  that  of  the 
normal  voltage.  I  therefore  endorse  what  Mr.  Field  says  at  the  end  of 
his  paper  that  the  oscillatory  effects  are  those  that  need  most  to  be 
studied  by  means  of  the  apparatus  we  have  at  hand,  notably  the  oscil- 
lograph. 

{Communicated) :  In  criticising  Mr.  Field's  equation  on  page  6qi,  I 
was  under  the  impression  that  he  was  using  the  terms  involving  the 
resistance,  self-induction,  and  capacity  as  vector  quantities,  in  which 
case  the  expression  for  the  ratio  of  the  squares  of  the  pressures  at  the 
two  ends  of  a  transmission  line  on  open  circuit  is  of  the  form 

i(cosh2R/  4-  i), 

R  being  a  constant  involving  the  capacity,  etc.,  and  /  the  length  of  the 
line.  I  see  now,  however,  that  he  is  not  using  vectors  but  numerical 
quantities,  in  which  case  the  expression  is  of  the  form 

i  (cosh  2  P  /  4-  cos  2  Q  /). 
Q/  is  the  angle  of  advance  in  phase  of  the  pressure  as  the  sending  end 
is  approached ;  for  maximum  resonance  this  angle  is  - ,  so  that  this 
expression  then  becomes 

i(cosh  2P/—  i), 

and  this  is  the  equation  given  by  Mr.  Field,  putting  cosh  for  the  more 
complicated  exponential  terms  used  in  his  paper,  the  sign  being  rightly 
negative. 

Mr.  G.  L.  Addenbrooke  :  My  remarks  will  bear  upon  rather  a  Mr.  Adden- 
different  part  of  the  subject  to  that  alluded  to  by  the  last  speakers. 
The  paper  covers  so  much  ground  that  it  is  impossible  to  deal  with  all 
the  points  in  it.  As  I  have  had  considerable  experience  in  testing 
cables  for  what  is  called  dielectric  hysteresis,  perhaps  some  account  of 
what  I  have  done  might  be  interesting.  My  own  work  began  in  the 
following  way.  Dr.  Muirhead  some  two  years  ago  lent  me  some  of  his 
special  condensers  for  the  purpose  of  investigating  the  losses  which  took 
place  in  them.  I  had  been  too  busy  to  do  anything  with  them  up  to  the 
date  of  Mr.  Morde/s  Institution  paper  two  years  ago,  but  startled  by 
his  results  I  forthwith  began  some  tentative  experiments  which  I  men- 
tioned in  the  debate.  Shortly  after,  I  received  a  communication  from 
the  Henley  Telegraph  Cable  Co.,  who  were  concerned  from  a  com- 
mercial standpoint,  and  who  were  rather  upset  by  the  possibility  of  this 


brooke. 


766  CONSTABLE  AND   FAWSSETT  [April  2Srd, 

Mr.  Adden-  large  dielectric  hysteresis  loss.  The  result  was  that  they  asked  me  to  make 
some  investigations  at  their  works  on  the  subject.  The  first  question 
which  arose  was,  how  these  experiments  should  be  made.  That  really, 
I  think,  is  the  matter  which  is  before  us  at  the  present  moment,  because 
it  is  not  much  good  having  experiments  made  until  we  are  pretty  certain 
that  the  means  used  for  making  the  experiments  are  likely  to  give  fairly 
correct  results.  I  therefore  went  into  this  matter.  My  idea  was  to 
employ  the  electrostatic  system  of  measurement,  which  I  described 
generally  at  the  International  Congress  at  Paris  two  and  a  half  years  ago. 
When  I  came  to  look  into  it,  it  seemed  that  it  would  be  suitable,  and 
also  that  it  was  adapted  to  meet  the  following  very  important  point. 
Going  into  the  calculations  with  regard  to  air  core  transformers  for 
insertion  in  the  circuit,  I  found  it  usually  meant  that  you  must  have 
three  or  four  tnicrofarads  capacity  in  the  cable,  in  order  to  keep 
your  air  core  transformer  within  reasonable  limits,  which  of  course 
means  a  long  length  of  cable,  which  it  is  very  troublesome  to  deal 
with  and  is  not  very  commercial.  By  using  the  electrostatic  system, 
even  as  the  system  stood  intended  for  ordinary  work,  I  found  one 
could  go  down  to  half  microfarad  with,  it  appeared  to  me,  a  fair 
chance  of  being  pretty  accurate.  There  is  no  doubt  that  by  special 
arrangements  it  is  possible  to  measure  electrostatically  the  loss  in  very 
smaU  capacities  indeed— in  fact,  since  the  date  of  my  experiments,  in  a 
paper  in  the  journal  of  the  American  Institute  of  Electrical  Engineers f}AT, 
Miles  Walker  described  how,  by  means  of  a  special  electrometer  used 
in  order  that  the  high  pressure  might  be  directly  applied  to  it,  he  has 
been  able  to  make  dielectric  hysteresis  measurements  on  slabs  a  foot  or 
two  square.  Therefore  it  is  clear  that,  apart  from  its  suitability  other- 
wise, the  electrostatic  system  has  very  great  advantages  for  the  com- 
mercial measurement  of  dielectric  hysteresis,  because  we  can  deal  with 
very  moderate  lengths  of  cable. 

My  apparatus  being  set  up  at  Messrs.  Henley's,  arrangements  were 
made  for  carrying  out  tests  from  2,000  up  to  about  6,000  volts,  and  I  will 
give  you  a  few  specimens  of  them.  About  '9  of  a  microfarad  of  un- 
armoured  lead-covered  concentric  cable  was  tested  between  the  inner 
and  outer.  I  may  say  that  the  arrangements  at  Messrs.  Henle3r's  did 
not,  unfortunately,  permit  of  a  constant  periodicity  in  all  tests  being 
obtained,  because  they  had  to  vary  the  speed  of  the  alternator  to  some 
extent  to  get  the  different  voltages,  so  that  the  experiments  are  not  so 
comparable  directly  as  they  might  have  been,  but  when  allowance  is 
made  for  this  they  all  come  very  close  to  each  other.  The  results  I 
got  are  given  in  Table  I.  It  is  to  be  noted  that  the  power-factor 
gradually  rose  as  the  voltage  rose.  Another  point  that  turned  up  in  these 
experiments  was  that  the  results  are  all  somewhat  lower  than  those 
published  by  Mr.  Mather,  which  were  also  conducted  on  paper  cables, 
and  which  he  mentioned  in  dealing  with  Mr.  Mordey's  paper.  Of  course 
there  may  be  different  sorts  of  paper,  but  as  most  cable  makers  deal 
with  the  same  class  of  paper,  I  did  not  think  the  difference  could 
altogether  be  accounted  for  that  way.  The  question  therefore  arose 
whether  the  difference  was  due  to  differences  of  measurement  or  to  the 
material.    Of  course,  also,  there  might  have  been  possible  differences 


19(».] 


AND   FIELD  :  DISCUSSION. 


767 


due  to  the  wave  forms  that  were  used  in  the  experiments.  Unfortu- 
nately, as  regards  this,  I  had  not  the  means  at  my  command  at  the  time 
of  ascertaining  what  these  forms  were,  but  I  doubt  if  this  can  account 
for  all  the  difference.  However,  while  I  was  still  considering  this 
question  some  measurements  had  to  be  made  at  Wood  Lane  on  a  large 
inductive  resistance  which  I  designed  for  Messrs.  Willans  and  Robinson 
for  enabling  alternators  to  be  tested  at  proper  power  factors  and  which 
was  specified  to  carry  a  certain  current  for  six  hours  at  5,000  volts  without 
undue  heating.     From  the  ordinary  calculations  on  a  resistance  of  this 


Mr.  Adden- 
brookc. 


TABLE  I. 

Cable  Tests  at  W.  T.  Henley's  Telegraph  Works,  Ltd. 

Capacity  '9  mf.     Unarmoured  lead-covered  C.C.     Test  between  Outer 

and  Inner, 


Volts. 

Amperes. 

Watts. 

Periods. 
287 

Power  Factor. 

Actual. 

Calculated. 
•33 

Per  cent. 

2,040 

•24 

5-1 

1*04 

2,000 

•388 

•536 

IO-4 

48 

1-34 

3,000 

•36               •      -486 

18 

29 

167 

3,000 

•55               7 

24 

41 

I '46 

4,000 

•36               -452 

267 

20 

1-86 

4.040 

715     !      -965 

47 

43 

1-63 

1         5700 

•6          1        755 

60-4 

23 

172 

TABLE   II. 

Cable  Tests  at  Wood  Lane. 

Capacity.     Unarmoured  3  Core.      Tests  between  Cores  A,  B,  C. 


Vdts. 


5,000 
2,500 
2,500 
5,050 


Amperes. 

Actual. 

Calculated. 

Ill 

•863 

•637 

•432 

•95 

•69 

1-68 

1-38 

Watts. 
50 

i8-5 

32-5 
102 


50 
50 
50 
50 


Power  Factor, 
per  cent 


Cores  used. 
•9 

I'lO 

1*37 

V2 


768  CONSTABLE   AND   KAWSSETT  [April  23rd, 

Mr.  Adden-    sort,  made  for  me  by  Mr.  Berry  of  the  British  Electric  Transformer 
*^  ^'         Company,  we  came  to  the  conclusion  that  the  power  factor,  including 
the  losses  in  the  iron,  ought  to  be  about  4  per  cent.,  and  the  instruments 
correctly  indicated  about  4  per  cent.    Therefore  I  think  this  is  one 
fairly  strong  reason  for  sajring  that  the  instruments  were  capable  of 
measuring  power  factors  of  this  sort  with  close  accuracy.    In  the  case 
of  Mr.  Miller's  cable,  which  is  a  three-phase  cable,  it  was  tested  at  5,000 
volts  and  2,500  volts.    When  tested  between  one  core  and  the  other  the 
hysteresis  loss  came  out  at  about  1*2  per  cent.,  and  in  one  case  as  high 
as  1*37  per  cent.    Again,  as  in  Table  II.,  the  results  are  comparable 
with  the  other  results  I  obtained.    This  was  a  British  Insulated  Wire 
Compan/s  cable  of  the  same  kind  that  Mr.  Mather  was  experimenting 
with.     Having  arrived  at  this  point,  I  thought  I  would  check  my  work- 
ing by  testing  with  an  air  core  transformer,  that  is  to  say,  using  the 
electrostatic  system  and  putting  an  air  core  transformer  in.     For  that 
purpose  Mr.  Savage,  of  Henley's,  was  good  enough  to  have  one  con- 
structed of  flexible,  of  which  they  are  makers.   Dr.  Fleming,  in  his  book 
on  electric  testing,  has  put  forward  an  air  core  transformer  as  an  excel- 
lent means,  which  it  undoubtedly  is,  of  finding  out  whether  a  wattmeter 
indicates  properly  on  low  power  factors  because  you  can  with  it  get  a 
power  factor  as  low  as  3  per  cent.     Having  this  air  core  transformer,  it 
occurred  to  me  that  I  would  test  my  own  wattmeter  with  it.    This  I 
accordingly  did  at  Messrs.  Henley's  before  applying  it  to  the  cable. 
The  result  was  that  when  I  came  to  work  out  the  experiment  it  appeared 
as  if  there  was  some  loss  in  the  air  core  transformer  itself.     In  the 
debate  on  Mr.  Mordey's  paper  it  was  taken  as  an  axiom  that  there  was 
no  loss  in  the  air  core  transformer.     Not  being  certain  about  this,  I  got 
the  air  core  transformer  sent  up  to  my  own  laboratory  in  Victoria  Street, 
where  I  had  the  Deptford  current.     It  was  again  tested  at  about  double 
the  periodicity  at  which  it  was  tested  at  Messrs.  Henley's.    The  result 
was  that  the  loss  went  up  somewhere  about  as  the  square,  which  it 
would  do  if  that  loss  was  due  to  eddy  currents.     I  may  say  that  in  this 
case  the  loss  was  of  the  following  character.    The  whole  weight  of  the 
copper  in  the  air  core  transformer  was  somewhere  about  one  hundred- 
weight, and  the  loss  I  got  at  89  periods  was  about  36  watts,  uc,  about 
one-third  of  a  watt  per  pound.    When  you  come  to  consider  the  very 
large  number  of  ampere  turns  there  are  on  such  a  transformer,  and 
what  a  very  strong  field  there  is,  it  does  not  seem  impossible  that 
there   should  be  a  loss  of  this  sort.      In  my  case,  too,  the   flexible 
wire,  which  was  of  the  ordinary  character,  happened  to  be  very  new. 
In  Mr.  Mather's  case  he  used  an  air  core  transformer  of  solid  No.  14 
copper,  as  far  as  I  understand.     I  see  from  calculations  that  during  his 
tests  he  must  have  had  12,000  ampere  turns  on  the  coil,  which  makes  a 
very  strong  field.     It  seems  quite  possible  that  he  may  have  lost  50 
or  60  or  even  more  watts  in  80  lbs.  of  copper,  which  deducted  would 
make  his  results  nearly  the  same  as  mine.     I  do  not  wish  to  cavil 
at  Mr.  Mather's  figures.     I  think  he  did  his  experiments  somewhat 
hurriedly,  and  that  to  have  got  as  near  as  he  did  in  the  time  was  almost 
a  feat,  because  it  is  a  very  difficult  thing  to  get  reliable  experiments 
with  this  dielectric  hysteresis  work.     Perhaps  I  may  be  allowed  to  put 


1903.]  AND  FIELD:  DISCUSSION.  769 

my  results  into  ordinary  figures,  because  I  think  it  is  very  important  we   MrAdden- 

should  recognise  that,  at  any  rate  for  practical  purposes,  the  dielectric 

hysteresis  loss  in  itself  is  not  very  serious.    In  the  case  of  Mr.  Miller's 

cable,  which  was  a  three-phase  feeder,  2^  miles  long,  working  at  5,000 

volts,  the  actual  loss  was  about  100  watts,  or  40  watts  per  mile.    I  may 

say  that  that  was  tested  without  any  load  on,  and  therefore  perhaps  we 

had  rather  a  bad  curve,  in  fact,  the  main  was  actually  tested  afterwards 

by  Mr.  Duddell  with  the  oscillograph,  and  the  results  were  shown  on 

the  screen  at  the  last  meeting.     Unfortunately  I  cannot  say  now  which 

of  Mr.  Miller's  cables  the  test  was  made  on,  but  it  may  be  of  interest  to 

know  that  one  of  Mr.  Duddell's  results  is  the  wave  with  which  my  tests 

were  made. 

There  are  one  or  two  general  conclusions  I  should  like  to  mention. 
On  another  occasion  a  fresh  set  of  cables  were  put  up  for  experiment. 
Unfortunately  I  was  not  there  myself,  but  my  assistant,  Mr.  Robinson, 
who  really  works  my  instruments  better  than  I  do  myself,  conducted 
them.  In  this  case  there  was  an  iron  sheath  outside  the  cable,  and  the 
whole  of  the  results  came  out  higher  than  in  other  cases.  As  far  as  I 
know  the  cables  were  exactly  the  same  ;  this  bears  out  some  results  that 
have  been  given  in  the  paper  we  are  discussing.  I  was  rather  afraid  to 
publish  these  particular  results  at  the  time,  as  my  theoretical  friend 
polled  a  long  face,  but  as  the  matter  has  been  brought  forward  in  an- 
other form,  I  mention  that  in  that  particular  set  of  experiments  we  did 
get  30  or  40  per  cent,  increase  in  the  loss  when  the  cable  was  covered 
with  an  iron  sheath.  There  is  afnother  general  point  which  I  think  is 
worth  bringing  forward  with  regard  to  this  dielectric  hysteresis  loss. 
These  losses  go  up  with  the  voltage  to  some  extent ;  as  a  matter  of  fact 
the  voltage  on  one  occasion  was  carried  out  nearly  as  high  as  11,000 
volts,  or  as  much  as  the  cable  would  stand,  with  a  view  of  seeing  what 
would  happen.  The  watt  losses  go  up  more  than  proportionally,  so  that 
if  you  keep  the  wattmeter  on  and  watch  it,  it  really  forms  a  sort  of 
guide  to  what  is  going  on  in  the  cable,  and  when  you  get  near  the 
breaking  point  you  get  a  very  great  increase  of  the  watt  losses.  I  am 
inclined  to  think  that  a  measurement  of  this  class  may  be  very  useful  in 
testing  cables  as  to  what  they  are  likely  to  stand,  in  lieu  of  simply  putting 
on  a  breakdown  voltage,  or  say  two  or  three  times  the  working  voltage. 
In  testing  a  boiler,  no  one  would  think  of  testing  it  up  to  its  breaking 
pressure,  as  to  do  this  would  cause  permanent  damage ;  and,  in  the 
same  way,  by  putting  too  high  a  pressure  on  a  cable  its  resisting  powers 
may  be  permanently  injured,  but  tests,  at  a  few  gradually  increasing 
voltages,  of  the  watt  loss  with  an  alternating  current  will  enable 
a  curve  to  be  constructed  from  which  the  behaviour  of  the  cable  can 
be  seen  and  the  point  beyond  which  it  is  undesirable  to  press  the 
voltage  can  be  predicted. 

Mr.  C.  P.  Sparks  :  The  two  papers  before  us  show  how  much  we  Mr.  Sparks, 
are  indebted  to  Mr.  Duddell  for  the  oscillograph.  I  regret  to  have  to 
say  this,  after  so  many  other  speakers  have  mentioned  the  matter,  but 
as  I  have  worked  with  him  a  good  deal,  I  feel  how  much  we  are 
indebted  to  him  for  such  an  efficient  instrument  to  attack  some  of  the 
more  obscure  problems  in  connection  with  transmission  work.     Mr. 


770  CONSTABLE  AND   FAWSSETT  [April  23rcl 

Mr.  Sparks.  Field's  paper  brings  prominently  before  us  the  diflFerence  between  the 
modern  three-phase  generators  with  an  irregular  wave  form,  and  the 
old  type  of  singleiphase  machines.  In  Mr.  Field's  paper,  the  author 
directs  attention  to  the  advisability  of  localising  the  characteristics 
of  each  system  with  the  oscillograph.  I  cordially  endorse  his  recom- 
mendation. Some  three  years  ago,  my  attention  was  directed  to  the 
effect  of  running  up  an  excited  generator  on  mains  of  high  capacity 
when  it  was  found  that  as  the  frequency  rose  the  current  passing  into 
the  mains  rose  suddenly  to  a  high  value,  and  then  fell  with  increasing 
pressure  and  frequency.  This  occurred  twice  before  the  working  fre- 
quency and  pressure  were  reached.  The  oscillograph  at  once  showed 
what  was  happening.  Some  tests  which  Mr.  Duddell  carried  out  for  me 
with  the  oscillograph,  with  the  moving  film,  showed  that  all  variations 
in  the  number  of  mains,  generators,  and,  in  our  case,  throw-up  trans- 
formers should  be  made  at  standard  frequency.  Hence  it  is  usually 
dangerous  to  energise  a  main  by  running  up  from  a  separate  generator 
or  motor-generator,  unless  the  working  frequency  be  reached  before 
the  alternator  is  excited.  At  the  Deptford  station,  Mr.  Partridge  intro- 
duced ten  years  ago  the  method  of  energising  the  mains  through  a 
transformer,  the  secondary  of  which  was  gradually  short  circuited. 
Tests  showed  this  method  to  be  safe,  so  long  as  the  resistance  of  the 
secondary  did  not  fall  below  a  critical  value.  The  use  of  such  an 
apparatus  is  generally  limited  to  generators  of  the  copper  armature 
type,  owing  to  the  absence  of  harmonics,  and  this  system  cannot 
generally  be  applied  to  the  present  form  of  three-phase  generators. 
The  safest  method  to  switch  on  a  main  is  through  a  non-inductive  water 
resistance,  which  is  gradually  cut  out  over  a  period  of  a  quarter  of  a 
minute.  Last  year  Mr.  Duddell  took  records  of  switching  on  cables 
under  these  conditions,  and  it  was  found  that  as  long  as  a  period  of 
something  like  a  quarter  of  a  minute  was  taken  no  undue  rise  of 
pressure  occurred  in  switching  on  cables,  the  longest  length  being  14^ 
miles.    The  actual  length  tested  was  something  like  8  miles. 

The  modern  oil  break  switch  efficiently  disconnects  the  feeders 
under  normal  conditions  of  load.  Mr.  Duddell  took  records  which 
showed  that,  as  pointed  out  by  a  previous  speaker,  the  current  is 
apparently  always  broken  at  the  zero  point,  and  under  all  normal  con- 
ditions the  circuit  was  broken  without  any  dangerous  rise  of  pressure. 
The  most  dangerous  operation  is  the  removing  of  a  short-circuited 
feeder,  as  in  addition  to  the  heavy  current  to  be  broken  the  frequency 
of  the  station  may  be  affected.  Up  to  now  the  only  really  safe  con- 
dition to  remove  such  a  feeder  is  by  keeping  your  frequency  up, 
and  reducing  the  pressure  momentarily  in  order  to  disconnect  the 
feeder. 
Mr.  Mr.  A.  Campbell  :  With  regard  to  Mr.  Field's  method  of  testing 

CampbciL  whether  his  water  resistance  was  non-inductive  or  not,  I  think  he 
might  have  done  so  more  easily  by  trying  if  at  every  moment  the 
ordinates  of  the  current  curve  had  a  constant  ratio  to  those  of  the 
voltage  curve.  If  this  is  not  the  case,  the  ^circuit  is  not  non-inductive. 
(Communicated) :  The  simpler  method  would,  however,  give  no 
indication  of  the  value  of  the  power-factor. 


1903.] 


AND   FIELD:   DISCUSSION. 


771 


Thornton. 


Mr.  W.  DuDDELL  :  Mr.  Campbell  has  pointed  out  that  the  two  curves  Mr.  DuddcU. 
should  be  exactly  similar.  Unfortunately,  for  watt  meter  measurements 
where  considerable  accuracy  is  required,  an  error  of  one  minute  of  a 
degree  is  a  serious  matter  in  the  lead  or  lag  of  the  current  through  the 
resistance.  One  minute  of  a  degree  is  ^th  of  li^jth,  or  izjiiyTjth  of  a 
half  period.  I  do  not  think  it  is  possible  to  plot  a  wave  form  with  suffi- 
cient accuracy  to  show  a  lag  or  lead  of  that  order.  I  am  afraid  some 
other  method  has  to  be  used,  such  as  employing  a  very  high  frequency 
in  order  to  determine  such  small  angles. 

Dr.  W.  M.  Thornton  (communicated) :  It  is  to  be  regretted  that  Dr. 
Mr.  Field  was  unable  to  make  observations  at  the  generator  end  of 
the  cables,  or  on  the  high-tension  side  in  the  sub-station.  There  can 
be  little  doubt,  after  comparing  this  and  Messrs.  Constable  and  Faws- 
sett's  paper,  that  the  harmonics  of  Curve  XV.  are  chiefly  due  to  the 
capacity  of  the  cables ;  but  resonance  is  so  violent  and  sudden  a  pheno- 
menon that  one  is  impelled  to  ask  whether  there  may  not  be  any  other 
explanation. 

As  I  understand  the  method  of  experimenting,  the  curves  were  taken 
from  the  low-tension  side  of  a  175  k.w.  transformer,  unloaded.  There 
is  then  entering  the  cables  the  charging  current  together  with  a  small 
transformer  current.  But  the  secondary  voltage  of  a  transformer  is 
proportional  to  the  primary  current,  and  therefore  any  disturbance  of 
this  by  the  distributed  capacity  of  the  cables  will  be  inevitably  felt  on 
the  secondary  side,  though  the  conditions  may  be  far  from  resonance. 

According  to  this  view,  the  greater  the  capacity  of  the  cables 
between  generator  and  transformer,  the  greater  would  be  the  amplitude 
of  the  harmonics  on  the  voltage  wave  observed  on  the  low- tension  side 
of  the  transformer. 

The  remarkable  capacity  currents  caused  by  strong  harmonics  can 
be  seen  by  drawing  the  rate  of  change  of  the  voltage  against  the  gene- 
rated wave  :  this  representing  the  current  to  a  suitable  scale. 


The  intensity  of  the  harmonics  depends  very  much  on  excitation,  and 
one  is  led  to  ask  whether  the  conditions  of  excitation  were  precisely  the 
same  in  Curves  XV.,  XVI.,  XVII.,  XIX.  They  are  widely  separated  in 
time,  and  it  is  possible  that  all  the  conditions  might  not  have  been 
repeated,  especially  if  the  tests  were  made  in  the  early  morning  on  a 
very  light  load. 


772 


CONSTABLE  AND   FAWSSETT 


[April  2ard, 


Dr. 
Thornton, 


Mr. 

Atchison. 


With  regard  to  the  remark  on  page  655,  that  the  field  currents  are 
not  much  disturbed  by  armature  reaction,  I  have  found  that  a  variation 
of  5  per  cent,  is  common  in  a  separately  excited  three-phase  bi-polar 
converter,  and  I  should  think  that  in  a  multi-polar  machine  on  full  load 
the  effect  would  be  even  more  marked  on  account  of  the  relatively 
smaller  time-constant  of  the  windings. 

Harmonics  in  the  voltage  wave,  on  reaching  the  undisturbed 
magnetic  circuit  of  a  converter,  will  reproduce  the  magnetic  conditions 
which  started  them.  And  if  the  iron  is  not  saturated,  the  disturbance  so 
caused  may  be  sufficient  to  increase  the  amplitude  of  the  ripple  in  the 
continuous  voltage.  This  would  account  for  the  large  ripples  recorded, 
and  they  should  be  larger  the  greater  the  angle  of  lag.* 

On  page  655  Mr.  Field  attributes  the  smoothing  out  of  harmonics 
when  two  or  more  generators  are  in  parallel  to  the  increased  inductance 
diminishing  resonance.  I  made  observations  in  the  Wallsend  power- 
house of  the  Newcastle  Electric  Supply  Co.  two  years  ago  which  led 
me  then  to  believe  that  the  obliteration  of  harmonics  which  ^^as  alwa3rs 
noticed  when  several  generators  were  in  parallel,  was  really  caused  by 
difference  of  phase  in  the  respective  machines,  for  on  tracing  a  wave 
with  strong  harmonics,  displacing  it  a  few  degrees  from  the  original 
and  taking  the  mean,  the  harmonics  in  the  resultant  wave  are  much 
less  prominent.  This  small  difference  of  phase  may  be  the  result  of 
variable  turning  moment  and  will  then  give  rise  to  synchronising  cur- 
rents which  usually  reverse  in  time  with  the  engine ;  a  change  in 
excitation  of  one  of  the  machines  in  order  to  distribute  the  station  load 
as  desired,  will  produce  the  same  interchange  of  current  which  will 
now,  however,  not  change  sign. 

The  commencement  of  Part  II.  deals  with  the  growth  and  decay  of 
currents  in  large  inductive  circuits.  I  would  refer  Mr.  Field  to  a 
paper!  read  before  the  Newcastle  Section  last  session,  in  which  an 
oscillograph  was  used  for  the  same  purpose,  and  where  I  gave  a  more 
complete  analysis  of  the  curves  obtained. 

Mr.  A.  F.  T.  Atchison  (  communicated) :  Mr.  Field's  very  interesting 
paper  brings  before  the  notice  of  electrical  engineers  the  existence  in 
practice  of  some  phenomena  which  have  hitherto  been  considered  as 
possessing  chiefly  theoretical  interest.  The  oscillograph  is  an  instrument 
which  opens  out  great  possibilities  for  the  investigation  of  phenomena 
taking  place  in  alternating-current  circuits,  and  it  is  of  special  value  in 
revealing  the  many  secondary  effects  which  are  ignored  in  the  ordinary 
mathematical  treatment  of  the  subject  such  as  is  given  in  the  greater 
proportion  of  our  text-books.  This  treatment  of  alternating  currents  is, 
and  will  always  remain,  one  of  the  most  striking  applications  of  mathe- 
matical analysis  to  practical  work,  but  researches  such  as  those  of  Mr. 
Field  and  others,  assisted  by  the  oscillograph,  serve  to  show  that  the 
common  methods  of  calculating  alternating-current  problems,  though 
correct  in  the  main,  are  necessarily  somewhat  superficial  and  incom- 
plete.   One  of  the  chief  omissions  in  the  ordinary  theory  is  the  neglect 


•  The  Electrician^  Jan.  30,  1903,  p.  609. 
t  /61V/.,  April  and  May,  1902. 


THE  NEW  YORK 

PUBLIC  LIBRARY 


-■*         lFNO> 


S*  Mr. 

^      Atchison. 

r 


.    Mr.  Mather. 


Fig.  K. — Capacity  90  m.f. 


Fig.  O. — 2725  m.f. 
Exact  Resonance  vvitli  5th  Harmonic. 


Fig.  S.— 3675  m.f. 


Fig.  L. 


:f 


P.D.  AND  Cl'RREN'T  OSCILLOGRAMS  FROM  . 


ircuit. 


19080 


AND  FIELD;  DISCUSSION. 


778 


of  the  change  in  wave-form  which  may  occur  under  certain  conditions*  Mr. 
and  which  Mr.  Field  has  brought  before  our  notice  in  his  admirable  paper.      ^  ^^' 

The  change  of  wave-form  which  may  result  from  resonance  with 
high  harmonics  or  "  ripples  "  of  the  fundamental  wave  through  capacity 
of  certain  values  existing  in  the  circuit  are  very  interesting,  and  are 
shown  very  clearly  by  the  oscillograph.  The  effects  however  may  be 
very  much  more  important,  when  resonance  occurs  with  lower 
harmonics. 

As  an  example  of  the  great  extent  to  which  these  harmonics  may  be 
brought  into  prominence,  I  give  a  series  of  oscillograms  taken  (with  a 
Blondel  double  oscillograph)  from  an  alternator  working  on  capacity 
loads  of  different  magnitudes,  bringing  in  marked  resonance  with  the 
fifth  harmonic  (or  overtone  of  quintuple  frequency). 

The  E.M.F.  wave-form  of  the  alternator  on  open  circuit  is  shown  in 
Fig.  U,  containing  pronounced  triple  and  quintuple  harmonics,  and  is 
found  to  undergo  but  slight  alteration  on  a  non-inductive  load.  A 
gradual  increase  of  capacity,  however,  gives  rise  to  the  series  of  wave- 
forms given  in  Figs.  K  to  T ;  very  well-marked  resonance  with  the  fifth 
harmonic  taking  place  with  a  capacity  of  27*25  microfarads  in  circuit 
(Fig.  O) ;  the  current  during  this  stage  being  practically  a  simple  sine 
wave  of  5  times  the  fundamental  frequency  of  the  alternator,  each 
component  being  naturally  in  quadrature  with  the  corresponding  peak 
and  hollow  in  the  P.D.  wave.  A  further  increase  of  capacity  destroys 
the  resonance,  as  would  be  expected,  and  the  wave-forms  become  more 
normal.  Even  at  resonance  with  the  fifth  harmonic  the  rise  of  voltage 
across  the  alternator  terminals  amounted  to  43  per  cent,  (rising  from 
200  to  286),  and  had  I  been  able  to  increase  the  capacity  still  further, 
so  as  to  bring  about  resonance  with  the  third  harmonic,  no  doubt  the 
effects  might  have  been  magnified  to  an  even  greater  extent.  The  rise  of 
voltage  is  of  course  partly  due  to  the  fact  that  the  machine  is  supplying 
a  leading  current  and  is  therefore  working  with  a  strengthened  field. 

It  is  interesting  to  calculate  the  value  of  the  "  apparent  reactance  " 
of  the  alternator  armature,  from  the  value  of  the  capacity  which  gives 
rise  to  resonance.  The  frequency  of  the  fundamental  wave  was  57  (\J 
per  second,  and  thus,  taking  27*25  m.f .  as  the  capacity  corresponding  to 
exact  resonance  with  the  fifth  harmonic,  we  have 


2 T  X  5  X  57  X  2725  X  10'' 


ohms 


=  20'5  ohms  at  the  frequency  of  the  5th  harmonic 
(5  X  57  =  285  oj  per  sec). 

u.,  a  reactance  of  4*1  ohms  at  the  fundamental  frequency,  which  is  not 
very  different  from  the  value,  4*38  ohms,  which  was  obtained  from  the 
"open  '*  and  "  short-circuit  characteristics  "  of  the  machine — the  "  Syn- 
chronous Reactance  "  of  the  American  writers. 

Mr.  T.  Mather  (communicated) :  The  best  thanks  of  the  Institution  Mr.  Matiicr 
are  due  to  the  authors  for  putting  such  valuable  data  before  its  members. 


774  CONSTABLE   AND   FAWSSETT  [April  Sard, 

Mr.  Mather.  *  The  communications  will,  it  is  hoped,  induce  central  station  engineers 
to  pay  more  attention  to  the  testing  department  of  the  works  under 
their  control,  with  a  view  to  locating  and  reducing  the  various  losses 
which  inevitably  occur  in  the  distribution  of  electric  energy.  We  may 
also  hope  that  further  data  as  to  losses  in  generation  will  be  forth- 
coming. 

The  paper  is  specially  interesting  because  of  the  large  number  of 
wave-forms  met  with  in  actual  practice  which  it  contains.  These  illus- 
trate in  a  striking  manner  how  the  shapes  depend  on  the  load  on  the 
station  and  on  the  feeders  connected  with  the  'bus-bars.  Another 
valuable  part  of  the  paper  is  the  section  dealing  with  the  measurement 
of  dielectric  losses  in  cables  ;  and  Table  III.,  giving  the  "  constants"  of 
the  wattmeters  employed  in  the  tests,  is  instructive  in  showing  how 
much  the  so-called  "constants"  of  such  instruments  may  vary  when 
used  under  different  conditions. 

Every  one  who  has  attempted  to  measure  power  in  circuits  of  low 
power-factor  with  any  approach  to  accuracy  will  appreciate  the  diffi- 
culties met  with  by  the  authors  in  their  efforts  to  obtain  consistent 
results,  for  the  trouble  rapidly  increases  as  the  power-factor  decreases. 

The  Swinburne  wattmeter  behaved  better  than  the  Thomson  instru- 
ments, yet,  according  to  the  value  in  Table  III.,  the  "  constant"  of  the 
former  decreased  nearly  30  per  cent,  on  changing  from  a  leading  cur- 
rent, power-factor  0*129,  to  a  lagging  current  of  power-factor  0*034. 
This  would  indicate  that  the  pressure  circuit  was  inductive,  and  I  would 
ask  whether  the  instrument  ever  gave  negative  readings  on  any  of  the 
cables  tested  ? 

The  change  of  "  constant "  here  observed  is  quite  moderate  in 
amount  when  compared  with  that  shown  by  other  instruments  on  the 
market,  and  which  claim  to  be  non-inductive.  One  I  tested  some  two 
years  ago  gave  results  six  or  seven  times  as  high  as  they  should  have 
been  on  a  condenser  circuit,  and  about  one-third  of  the  correct  value 
on  a  chokei'.  The  true  "constant,"  i.e.,  the  number  by  which  the 
deflexions  of  the  wattmeter  have  to  be  multiplied  to  get  "  watts,"  was 
therefore  twenty  times  as  large  in  the  latter  case  as  in  the  former.  The 
wattmeter  itself  was  fairly  good,  and  the  fault  lay  in  the  pressure 
circuit  resistance  coils  supplied  with  the  instrument.  These  coils, 
although  wound  in  the  way  invented  by  Mr.  Swinburne  for  minimising 
induction  and  capacity,  are  decidedly  anti-inductive,  i.<?.,  the  current 
through  the  coils  leads  on  the  P.D.  between  the  terminals.  In  fact  the 
lead  was  quite  measurable  by  the  contact-maker  method  at  a  frequency 
of  100.  On  replacing  the  coils  by  another  resistance  of  better  design 
the  readings  of  the  wattmeter  became  correct  within  a  few  per  cent. 

As  Mr.  Addenbrooke  has  referred  to  the  measurements  of  dielectric 
hysteresis  by  the  aid  of  "  air  core  transformers  "  (ironless  chokers)  made  by 
Professor  Ayrton  and  myself  in  1901,  I  take  this  opportunity  of  answer- 
ing some  of  his  queries.  In  the  first  place  I  agree  with  Mr.  Addenbrooke 
that  the  value  of  the  power-factor  for  paper  cables  then  published  is 
somewhat  higher  than  the  average  for  high-tension  cables  of  that  make. 
I  would  also  point  out  that  although  our  measurements  of  power-factor 
gave  results  far  less  than  Mr.  Mordey's  tests,  our  low  values  were  some- 


1903.]  AND   FIELD:   DISCUSSION.  776 

what  higher  than  the  correct  ones.  One  reason  for  this  is  that  (as  was  Mr.  Mather, 
pointed  out  at  the  time,  Journ,  !.£,£,,  vol.  30,  p.  412)  the  cables  tested 
were  intended  for  low  pressures,  but  were  tested  at  2,000  volts.  The 
slope  of  potential  in  the  dielectric  was  therefore  greater  than  is  usual 
in  high-pressure  cables,  and  this  usually  means  greater  power-factor. 
Another  reason  why  the  low  value  we  gave  is  too  high,  is  that  the  eddy 
current  loss  in  the  choker  was  neglected  in  these  tests,  and  this,  as  I 
pointed  out  in  the  Electrician  (March  8, 1901,  p.  750),  makes  the  power- 
factor  appear  higher  than  the  true  value.  This  effect  of  eddy  currents 
loss  is  indicated  on  p.  413  of  the  Journal  (vol.  30),  for  the  tests  made 
without  the  choker.  Fig.  D,  gave  the  smallest  power-factor,  viz.,  0*023, 
whereas  those  with  the  choker,  Figs.  B  and  C,  gave  0*025.  Mr.  Adden- 
brooke's  estimate  of  the  eddy  loss  in  our  choker,  60  watts,  is,  however, 
too  liberal.  Possibly  this  is  due  to  his  taking  the  ampere-turns  on  the 
coil  as  12,000  instead  of  8,000.  A  third  reason  for  our  low  power- 
factors  being  in  excess  of  the  correct  values  is  found  in  the  fact  that, 
although  the  coils  used  in  the  pressure  circuit  were  the  most  perfectly 
non-inductive  resistances  then  made,  they  were  slightly  anti- inductive. 
This  caused  the  current  in  the  pressure  circuit  to  lead  on  the  P.D.,  and 
made  the  wattmeter  read  high  on  circuits  taking  leading  currents.  It 
will  therefore  be  seen  that  the  numbers  I  pubUshed  in  1901  for  the 
power-factors  of  paper,  indiarubber,  and  jute  cables,  although  only  a 
small  fraction  of  Mr.  Mordey's  value,  were  actually  higher  than  the  real 
ones. 

Since  1901  I  have,  with  the  kind  permission  of  Professor  Ayrton, 
tested  other  paper  cables  at  2,000  volts,  using  in  the  pressure  circuit  of 
our  wattmeter  the  improved  resistances  mentioned  by  Mr.  Duddell  in 
this  discussion  ;  the  power-factors  obtained  varied  between  0*015  and 
0*019. 

During  his  remarks  Mr.  Addenbrooke  said  one  of  the  disadvantages 
of  using  **  ironless  chokers  "  in  cable  tests  was  the  large  capacity  (three 
or  four  microfarads),  and  therefore  long  lengths  of  cable,  necessary  to 
produce  resonance.  In  this  connection  I  may  mention  a  choker  con- 
structed at  the  Central  Technical  College  two  years  ago,  and  referred  to 
in  the  Electrician  of  March  8,  1901  (p.  750).  This  coil  has  an  induc- 
tance of  nearly  6  henries,  and  will  balance  about  0*4  microfarad  at 
100  f\j  ;  it  contains  i  cwt.  of  No.  18  wire,  and  absorbs  only  24  watts 
at  2,000  volts.  The  question  of  a  choker  necessary  to  balance  a  small 
capacity  is,  however,  merely  a  matter  of  design,  and  there  is  no  diffi- 
culty whatever  in  making  a  choker  suitable  for  testing  1 10  yards,  or  even 
shorter  lengths,  of  cable. 

Considerable  improvement  in  sensitiveness  and  accuracy  has  been 
made  in  dynamometer  wattmeters  and  shunt  resistances  during  the  past 
few  years,  and  it  is  now  possible  to  measure  the  loss  in  short  pieces  of 
cable.  Twenty-yard  lengths  have  been  tested  with  comparative  ease. 
The  currents  taken  by  such  lengths  of  small  capacity  cables  were  very 
small,  but  were  easily  and  accurately  measured  by  shunting  an  electro- 
static voltmeter  with  non-inductive  resistances. 

Tests  have  also  been  made   (using  improved  apparatus)  on  con- 
densers, with  the  result  that  the  power-factor  pf  some  Swinburne 
Vol..  82.  61 


776 


CONSTABLE  AND   FAWSSETT 


[April  23rd, 


Mr.  Mather  condensers  were  found  to  be  below  o*oo8,  and  of  some  condensers 
made  by  the  late  Mr.  Cromwell  Varley  more  than  thirty  years  ago  below 
0*004.  For  much  assistance  in  these  tests  I  desire  to  thank  Messrs.  Few. 
Finnis,  Nesfield,  and  Selvey,  students  of  the  Central  Technical  College, 

It  is  of  great  interest  and  importance  to  notice  that  the  condensers 
made  by  Mr.  Swinburne  some  ten  years  ago  show  losses  very  much  less 
than  modern  cables.  This  is  highly  creditable  to  our  late  President, 
especially  as  the  dielectric  in  these  condensers  is  very  thin  compared 
with  that  on  high-tension  cables,  and  the  potential  gradient  in  the 
dielectric  correspondingly  great.  As  condensers  can  thus  be  made  with 
dielectric  loss  about  half  that  of  modern  cables,  it  should  be  possible  to 
reduce  the  power-factors  of  cables  to  half  the  values  now  usual.  Makers 
of  cables  will  doubtless  give  this  matter  their  careful  attention, 
especially  where  extra-high-tension  cables  are  concerned. 

In  connection  with  Mr.  Field's  paper  I  might  mention  a  simple  way 
of  detecting  which  harmonics  are  present  in  the  wave-form  of  a  machine. 
This  is  to  watch  the  ammeter  in  circuit  with  an  unloaded  cable  (or 
condenser)  as  the  machine  slows  down.  If  any  important  harmonics 
exist  the  reading  of  the  ammeter,  instead  of  falling  gradually,  will 
remain  steady,  or  even  rise  when  the  speed  reaches  a  value  which 
causes  any  particular  harmonic  to  resonate.  With  some  machines 
several  rises  may  be  observed  before  the  alternator  comes  to  rest* 
The  method  may  be  made  quite  safe  by  introducing  sufficient  non- 
inductive  resistance  in  the  circuit  to  prevent  the  rises  becoming 
excessive. 

Mr.  A.  D.  Constable,  in  reply,  said  :  I  have  to  thank  you,  gentlemen, 
on  behalf  of  Mr.  Fawssett  and  myself,  for  the  considerate  treatment 
which  has  been  accorded  to  our  paper,  notwithstanding  its  short- 
comings. Some  of  the  inconclusive  figures  given  in  Table  4,  with 
regard  to  cable  losses,  would  not  have  been  placed  before  the  Institu- 
tion had  it  not  been  for  the  fact  that  it  was  impossible  to  continue  the 
experiments  and  further  verify  the  results.  The  results  were  given  as 
obtained,  and  we  hoped  that  they  would  be  discussed,  with  a  view  to 
deciding  the  causes  of  the  discrepancies.  I  will  try  to  treat  the 
various  points  raised  as  far  as  possible  in  the  order  they  occur  in 
the  paper.  Mr.  Minshall  referred  to  the  cost  of  lost  units  being  very 
heavy  because  the  greater  proportion  takes  place  at  times  of  maximum 
load.  It  is  true  that  about  60  per  cent,  of  the  loss  occurs  at  times  of 
heavy  load.  That  means  in  this  particular  case  (where  the  total  loss 
is  22  per  cent.)  about  13  per  cent,  additional  plant  has  had  to  be  put 
in  to  supply  those  wasted  units,  beyond  what  is  necessary  for  the 
maximum  useful  load.  The  whole  annual  cost  of  this  13  per  cent, 
extra  plant  must  be  put  down  to  the  units  wasted  during  the  time 
it  is  running  only,  and  although  as  a  rule  the  actual  running  cost 
is  rather  less  during  heavy  loads  than  during  the  day,  the  total 
cost  may,  therefore,  be  high.  In  certain  cases  also,  where  it  is 
necessary  to  run  an  additional  generator  owing  to  the  day-load  losses, 
these  will  cost  more  than  the  average  per  unit  generated. 


Mr. 
Constable. 


*  See  Electrical  Review,  May  31,  1901,  pp,  915-917. 


1908.] 


AND   FIELD:   DISCUSSION. 


777 


A  question  was  asked  about  Table  i.  This  Table  includes  the  losses 
from  the  generator  terminals  to  the  feeder  terminals.  The  percentage 
(o'S)  is  small,  but  it  represents  an  expenditure  of  about  ;£8o  per  annum» 
so  that  if  ;f  200  or  ;f  300  additional  capital  outlay  would  save,  say,  one- 
third  of  the  loss,  it  would  be  worth  while  spending  it. 

Mr.  Duddell's  objections  to  diagrams  3  and  4  are  unfounded,  as  he 
hopes.  We  had  a  large  non-inductive  resistance  in  series  with  the 
pressure  coil  of  the  wattmeter  in  all 
cases,  and  also  in  series  with  the  volt 
coil  with  the  oscillograph,  but  it  is 
omitted  in  the  diagrams.  The  total  re- 
sistance of  the  wattmeter  shunt  circuit 
was  about  7,000  ohms,  so  that  the  pres- 
sure coil  is  taking  rather  less  than  i  per 
cent,  of  the  total  current  in  the  resistance 
R,,  Diagram  3.  In  connection  with 
Diagram  3,  Mr.  Duddell  asked  how  we 
obtained  the  power-factor  with  a  leading 
current  I  will  try  to  explain  this  by 
means  of  a  diagram. 

Ra  is  a  Don-inductive  resistance  in  series  with  the  wattmeter  current 
coil,  and  the  ciu-rent  in  it,  A^,  is  in  phase  with  the  applied  volts,  V. 
C  is  the  ironless  choker  with  resistance,  R,  and  in  series  with  it  is  the 
non-inductive  resistance,  R,. 

The  wattmeter  pressure  coil  is  connected  to  the  terminals  of  R„ 
the  voltage  across  which  is  V.    A,  is  the  current  in  C  and  R,. 

V  is  in  phase  with  A„  and  since  A,  lags  behind  V,  the  current  A,  is 
leading  with  regard  to  V. 

The  watts  absorbed  by  the  choker  =  A,*  R, 


Mr. 
Constable 


Fig.  v. 


Rx 


=  A.V; 


the  total  watts  in  the  choker  circuit  therefore  equal  A,  (A,  R  +  V),  the 
corresponding  volt-amperes  =  Ax  V;  therefore  the  power  factor  of  the 

choker  circuit  is  equal  to  -^}  -^r- — '  =  cos  9,  where  9  is,  by  the  usual 

definition,  the  equivalent  angle  of  lag  of  Ai  behind  V. 

The  watts  indicated  by  the  wattmeter  will  be  AaVK  cos  $,  where 
K  =  constant  of  instrument,  so  that — 


K=: 


Reading  _    Reading  X  V    /R.M.S.\ 
A,  V  cos  9  ~  K  (A,  R  +  V)  V  \ values/* 


If  now  we  are  not  dealing  with  sine  waves,  the  voltages  across  C  and 
R,  respectively  may  be  different  functions  of  the  time,  so  that  A,  R  and  V 
cannot  strictly  be  added,  but  with  the  wave  forms  used  in  the  calibration, 
the  error  tjjus  introduced  will  be  very  small. 

[Note  added  later, — I  am  now  obliged  to  admit,  on  further  con- 
sideration, that  the  possibility  of  errors  being  introduced  by  accepting 
this  calibration  may  be  greater  than  was  at  first  supposed.  In  reply 
to  Mr.  Mather's  query,  I  may  say  that  the  wattmeters  used  in  our 
experiments  did  not  at  any  time  give  a  negative  reading  on  the  cables 
tested.] 


778  CONSTABLE   AND   FAWSSETT  [April  23rd. 

Mr.  It  is  true  that  the  calibration  is  only  quite  correct  for  the  particular 

**  wave  forms  used,  and  in  the  cable  experiments  the  wave  forms  were 
sometimes  very  diflFerent.  We  do  not  profess  that  all  the  figures  in 
Table  4  are  absolutely  accurate,  but  what  we  attempted  to  show  and 
tabulate  in  Table  3  was  that  the  wattmeters  gave  an  approximately 
correct  reading  for  both  lagging  and  leading  currents  and  for  cousider- 
ably  different  wave  forms.  We  agree  with  Mr.  Duddell  that  the  watt- 
meter method  is  by  far  the  best  to  obtain  the  power  factor  in  a  cable  if 
a  wattmeter  can  be  obtained  which  will  indicate  watts  only  and  not 
concern  itself  with  several  other  things  as  well.  I  am  glad  to  hear  that 
such  an  instrument  has  been  devised  by  Mr.  Duddell.  The  motor 
alternator  method  might  be  of  use,  but  it  is  rather  complicated  and 
requires  a  number  of  simultaneous  readings  and  adjustments  to  make 
it  practicable.  Mr.  Mordey  rather  advocated  the  calorimetric  method, 
which  certainly  cannot  be  used  after  the  cable  is  laid,  and  if  the  cable  is 
coiled  in  a  tank  inaccuracies  are  introduced,  as  Mr.  Minshall  has  found. 
The  method  might  be  used  if  a  specially  lagged  trough  were  made,  of 
considerable  length,  as  suggested  by  Mr.  Mordey  and  Mr.  Minshall,  and 
the  temperature  rise  in  a  given  time  measured ;  but  even  in  the  worst 
cable,  No.  7,  the  watts  lost  per  yard  are  only  about  06,  so  that  there 
would  be  some  difficulty  in  measuring  the  temperature  rise  accurately 
in  an  iron  trough,  such  as  should  be  used. 

Mr.  Duddell's  vigorous  criticism  of  Table  4  was  perhaps  justified 
by  the  appearance  of  some  of  the  figures.  We  do  not  profess  that 
these  figures  are  all  even  approximately  accurate.  Where  great 
discrepancies  appear,  the  figures  are  inserted  to  show  what  diver- 
gence may  occur  even  in  experiments  made  with  care.  Cable  No.  7 
is  without  doubt  abnormal,  while  the  variations  in  Nos.  4,  7,  and  9 
are  hardly  larger  than  would  be  expected  from  the  conditions.  Cable 
No.  10  is  an  exception.  Of  the  two  very  different  values  obtained  fcM* 
that  cable,  the  second,  namely,  0*024,  was  obtained  with  the  choker 
in  parallel  with  the  cable,  and  is  therefore  probably  the  more  accurate. 
The  low  insulation,  2  rCt,  is  due  to  switch  base  leakage,  and  not  to  the 
cable.  In  the  case  of  experiments  i  to  13  the  figures  are  the  means  of 
several  sets  of  readings.  The  frequency  in  all  cases  was  60  r\j ,  within 
I  per  cent.  With  regard  to  cable  11,  Mr.  Duddell  accused  us  of 
arbitrarily  selecting  results  and  of  failing  to  draw  the  proper  inferences 
from  the  experiments.  The  reason  for  selecting  experiments  18  to  20 
in  preference  to  15  to  17  are  given  in  the  paper  on  p.  716.  These 
experiments  were  made  with  different  machines.  Nos.  18  to  20  were 
taken  with  a  120-kw.  machine,  whilst  Nos.  15-17  were  taken  with  a 
30-kw.  machine  of  the  same  type,  and  there  was  no  other  difference  to 
account  for  the  former  being  the  much  smoother  waves.  It  is  prac- 
tically impossible  to  work  out  oscillograph  curves  when  th^  waves  are 
very  peaked,  but  the  results  of  the  smoother  waves  should  be  fairly 
accurate,  though  we  do  not  suppose  that  either  result  is  quite  correct 
Unfortunately  we  had  no  suitable  wattmeter  available  at  the  time,  and 
there  has  been  no  opportunity  of  checking  the  results  since.  As  to  the 
effect  of  the  wave-form  on  hysteresis  loss,  we  prefer  to  judge  by  the 
majority  of  the  experiments,  which  show  there  is  npt  §uch  a  great 


190S.]  AND   FIELD  :  DISCUSSION.  779 

difference  as  experiments  15  to  20  indicate,  although  there  is  some  Mr. 
variation.  Mr.  Duddell  also  remarked  on  the  low  result  obtained  for 
the  watts  absorbed  by  cable  12.  We  only  obtained  900  watts,  whereas 
the  figure  should  have  been  about  1,100,  summing  up  the  watts 
absorbed  in  the  various  component  parts,  after  correcting  for  voltage. 
But  again  this  experiment  was  made  without  a  wattmeter,  and  so  there 
is  a  good  deal  of  possibility  of  error  in  working  out  the  results. 

Mr.  Field  questioned  Table  5.  In  that  table  the  figures  in  the  last 
column  were  calculated  from  data  obtained  by  experiment.  We  took 
the  readings  on  cable  No.  7  and  observed  the  watts  absorbed,  but  as 
this  was  an  abnormal  case,  we  wished  to  correct  them  for  a  hypothetical 
paper  cable.  The  results  are  therefore  only  approximate,  as  stated.  Our 
experience  goes  to  confirm  Mr.  Field's  remarks  to  the  effect  that  a 
dielectric  with  a  high  hysteresis  loss  has  a  low  disruptive  strength. 
With  regard  to  the  magnetic  field  stated  to  exist  round  a  cable,  since 
writing  the  paper  we  have  made  some  further  experiments.  A  large 
alternating  current,  250  amperes  at  60  C\J ,  was  passed  through  the 
inner  and  back  by  the  outer  of  50  ft.  of  cable  of  the  type  of  No.  11, 
Table  4,  in  a  straight  length.  At  the  centre  a  piece  of  cast-iron 
trough  6  ft  long  was  placed.  Three  feet  of  the  trough  had  the  cover 
removed  from  it.  A  search  coil  18  in.  by  5  in.,  consisting  of  200 
turns  of  fine  wire  connected  to  a  telephone,  was  fixed  (at  the  same 
distance  from  the  centre  of  cable)  (A)  over  the  uncovered  portion 
of  cable,  (B)  over  the  uncovered  portion  of  trough,  (C)  over  the 
covered  portion  of  trough.  In  position  (A)  the  noise  was  very  loud, 
at  (B)  it  was  much  less,  and  at  (C)  there  was  practically  silence. 
The  noise  in  position  (A)  was  roughly  the  same  as  that  produced 
by  a  current  of  2  amperes  in  a  long  straight  wire  at  the  same 
distance  from  the  coil  (about  2^  in.).  That  seems  to  show  that  there  is 
an  external  magnetic  field  which  is  practically  all  shielded  by  the  iron 
trough.  A  piece  of  concentric  armoured  cable  behaved  in  the  same  way, 
but  the  shielding  effect  of  the  thin  armour  was  slight.  Cable  7  has  the 
outer  conductor  of  a  rather  open  strand,  so  that  the  external  field  may 
be  greater  than  in  the  case  of  No.  11,  which  has  a  closely  laid  outer. 
(It  is  difficult  to  see  how  this  field  can  exist,  liowever.)  It  will  be  of 
interest  to  pursue  these  experiments  and  investigate  the  strength  of  field 
in  the  iron  trough  kt  ordinary  loads.  It  still  appears  possible  that  some 
of  the  apparent  dielectric  hysteresis  loss  is  really  iron  loss  in  the  case 
of  No.  7  cable. 

Mr.  Mordey  stated  he  thought  it  was  more  economical  to  allow 
several  transformers  to  share  the  load  than  to  keep  one  or  two  fully 
loaded.  We  admit  that.  Our  point,  however,  was  that  it  was  very 
wasteful  to  keep  many  transformers  on  at  times  of  no  load,  and  these 
times  make  up  the  greater  part  of  the  24  hours. 

Mr.  Andrews  referred  to  the  danger  of  switching  off  transformers. 
I  may  say  that  during  six  years  not  one  of  the  fifty  odd  transformers  in 
Croydon  has  broken  down  due  to  repeated  switching  off  and  on.  That 
they  are  all  of  the  oil-cooled  type  may  be  partly  responsible  for  this. 
Small  punctiu'es  in  the  insulation,  if  they  exist,  may  be  filled  up  with 
oil  before  the  transformers  are  again  used.    The  oil,  too,  will  act  as  a 


780  CONSTABLE  AND    FAWSSETT  [April  2Srd, 

Mr.  lubricant  and  prevent  abrasion  of  the  insulation  due  to  vibration  and 

alternate  expansion  and  contraction.  The  mean  temperature  of  the 
transformers  is  kept  down  by  the  practice  of  switching  off  transformers 
not  required.  With  reference  to  the  remarks  on  meters ;  in  direct- 
current  systems,  ampere-hour  meters  of  considerable  capacity  are 
obtainable  which  will  record  accurately  on  a  200-voIt  5-c.p.  lamp.  If 
there  are  no  very  satisfactory  alternating-current  ampere-hour  meters, 
it  is  possible  to  obtain  accurate  energy  meters  which  require  an 
exceedingly  small  shunt  current  and  which  have  no  moving  contacts. 
Meters  which  require  frequent  inspection,  cleaning,  and  adjusting 
cause  more  than  half  the  trouble  between  the  supply  authorities  and 
the  consumers. 

Mr.  Addenbrooke  has  mentioned  that  the  loss  in  a  cable  increases 
more  than  proportionately  to  the  rise  in  voltage.  We  have  found  that 
to  be  the  case  ;  in  fact,  in  some  experiments  we  made,  the  increase  has 
been  more  than  proportionate  to  the  square  of  the  voltage.  I  am 
glad  to  hear  that  Mr.  Addenbrooke  also  finds  a  considerable  increase 
in  the  loss  when  the  cable  is  surrounded  by  iron.  Mr.  Sparks  men- 
tioned the  dangers  of  running  up  an  alternator  on  a  cable  slowly. 
That  is  illustrated  by  curve  13,  sheet  C,  in  the  paper.  There  we 
had  an  alternator  running  at  about  half  speed  under  otherwise  ordinary 
conditions  on  a  cable,  and  the  voltage  rose  to  about  6,000  maximum 
on  a  2,000-volt  system. 

I  do  not  think  any  other  points  raised  remain  to  be  dealt  with,  and 
will  therefore  conclude  my  remarks  by  again  thanking  you  for  your 
kind  reception  of  this  paper. 

[Note  added  later. — In  all  cases  the  C'R  loss  due  to  the  capacity 
current  is  included  in  the  dielectric  hysteresis  loss,  its  value  being  only 
a  small  percentage  of  the  total.] 

Mi.  Field.  Mr.  M.  B.  FiELD  {in  reply) :  -  I  think  the  best  way  to  answer  the  many 

remarks  that  have  been  made  upon  my  paper  will  be  to  deal  first  with  the 
more  direct  criticisms,  and  after  that  to  cover  with  a  few  general  remarks 
the  further  comments  of  other  speakers.  Referring  first  to  Professor 
Hay,  I  certainly  grant  that  to  be  lax  with  one's  terminology  is  a  most 
serious  error  for  any  one  to  fall  into,  and  perhaps  I  am  to  a  certain  extent 
guilty  in  this  respect,  but  I  think  that  Professor  Hay  Ijas  rather  exagge- 
rated my  delinquencies.  First,  with  regard  to  the  secohm.  I  supp>ose 
I  should  not  defend  the  term,  as  it  has  now,  by  universal  consent,  been 
discarded,  but  it  seems  to  me  such  a  rational  term,  and  "  henry" 
seems  anything  but  that.  "  Secohm  "  gives  one  at  once  an  idea  of  what 
it  is.  Coefficient  of  self-induction  may  be  said  to  be  defined  by  the 
usual  equation — 

V  =  RC  -h  L"^ 

di 

and  is  really  the  back  E.M.F.  in  volts  in  a  circuit  when  the  current  is 
altering  at  the  rate  of  i  amp.  per  sec.     As  regards  its  dimensions  L  is 

*  Mr.  Field's  reply  to  the  discussion  on  his  paper  at  Glasgow  (see  p.  694) 
is  included  here. 


1903.]  AND   FIELD:   DISCUSSION.  781 

and  therefore  of  the  nature  of  a  time  multiplied  by  a  voltage   Mr.  Field. 


v^M 


/C 
and  divided  by  a  current,  hence  the  term  sec-ohm. 

Ohmic  Resistafice  :  The  adjective  "  ohmic  "  may  be  superfluous,  but 
no  one  can  call  it  misleading.  I  use  it  to  distinguish  resistance-proper 
from  "apparent"  resistance,  with  which  the  paper  deals  considerably. 
I  have  referred  to  certain  combinations  of  self-induction  and  capacity 
as  behaving,  as  far  as  the  external  circuit  is  concerned,  as  a  resistance 
of  so  many  ohms.  This  is,  of  course,  only  an  apparent  resistance,  as  in 
most  cases  it  is  only  true  at  one  particular  frequency  that  the  combina- 
tion could  be  exactly  replaced  by  a  resistance.  In  dealing  with  such 
combinations  I  maintain  thut  it  is  not  at  all  out  of  place  to  draw  the 
distinction  between  resistance-proper  and  apparent  resistance  by 
applying  the  epithet  "  ohmic  "  to  the  former. 

Self-induction  of  an  Alternator:  Professor  Hay  states  I  have  used 
this  term  in  more  than  one  sense.  I  consider  I  have  been  most  careful 
to  explain  the  exact  sense  in  which  I  have  used  it.  I  have  pointed  out 
what  I  consider  the  distinction  between  self-induction  and  armature 
reaction  is.  I  have  pointed  out  that  an  alternator  cannot  strictly  be 
said  to  have  any  true  coefficient  of  self-induction,  as  this  depends  on, 
and  varies  with,  the  saturation  of  the  field-magnet  system,  the  position 
of  same  relative  to  the  armature  coils,  and  the  strength  of  the  armature 
currents.  I  have  pointed  out  the  variable  nature  of  this  coefficient ;  I 
have  then  for  shortness  included  in  the  term  "self-induction"  the 
effect  of  armature  reaction,  saying,  "  In  talking  of  the  self-induction  of 
an  alternator  I  shall,  for  the  purpose  of  this  paper,  include  in  the  term, 
armature  reaction,  i.e.^  I  shall  refer  to  that  self-induction  (whether  with 
constant  or  variable  coefficient)  which,  inserted  in  series  with  a 
reaction  less  and  self-inductionless  machine,  would  give  the  same 
characteristics."    Surely  I  cannot  be  blamed  for  indefiniteness  here. 

Synchronous  Impedance :  This  is  an  American  term.  I  think  it 
implies  \yhat  it  is,  viz.,  the  impedance  at  synchronous  speed.  It 
includes  self-induction  and  armature  reaction,  being  determined  by 
the  comparison  of  the  short-circuit  armature  current  at  synchronous 
speed  at  a  given  excitation,  with  the  no  load  E.M.F.  at  same  speed 
and  excitation.    The  term  is  quite  a  well-known  one. 

I  was  somewhat  surprised  at  the  rather  dogmatic  way  Professor 
Hay  denied  the  correctness  of  the 

statement    on    page   662    that    the  ^  a       '' 

combination  (Fig.  W.)  behaves  under  pRRRmnn — vww^^ 

all  conditions,  as  far  as  the  external     ^i (=^ aaaaaaJ^* 

circuit  is  concerned,  as  a  resistance  k       ^  ^ 

of  r  ohms  provided  K  =  ^^     The  ^»^-  '^'• 

text  may  be  a  little  badly  worded  here,  but  when  I  say  that  this  is  true  for 
all  frequencies  and  for  periodic  and  unperiodic  functions,  it  is  perfectly 
evident  that  the  condition  represented  by  (9)  which  refers  to  one  particu- 
lar frequency,  has  nothing  to  do  with  the  matter.  I  did  not  attempt  to 
prove  my  statement  because  the  proof  is  to  be  found  elsewhere.  I 
thought  it  was  a  matter  of  common  knowledge,  for  certainly  Professor 


782  CONSTABLE  AND   FAWSSETT  [April  23rd, 

Mr.  Field,  Perry  has  been  in  the  habit  of  giving  this  case  as  an  example  to  his 
students  for  fourteen  or  fifteen  years.  The  proof  is  to  be  found  on 
page  247  of  Perry's  "Calculus."  This  combination  is,  however,  interest- 
ing from  many  points  of  view,  and  is  worth  study. 

In  the  first  place  we  see  that  if  energy  be  stored  either  in  the  self- 
induction  or  the  capacity,  and  this  be  allowed  to  discharge  in  the 
closed  circuit,  the  combination  is  the  critical  one  at  which  the  dis- 
charge just  ceases  to  be  oscillatory. 

Secondly,  however  V  may  vary,  the  total  energy  stored  in  the  seK- 
induction  at  every  instant  is  equal  to  that  stored  in  the  capacity, 
for  remembering  L  =  K  r*  we  may  write,  using  Professor  Perry's 
symbol  9-^ 

V  =  r(i  -h  Kre)C, 


-i'+K-y- 


The  energy  stored  in  the  self-induction  at  any  instant  is  4  L  C,*  ;  and  in 
the  capacity  i  K  ( V  —  r  C,)'.    But  it  is  clear  that  both  these  expressions 

may  be  written  in  the  form  —7 — ; jr-nrz  .  V' ;  hence,  however  V  may 

have  varied,  the  total  energy  stored  at  any  instant  as  expressed  by  this 
formula  is  the  same  both  for  self-induction  and  capacity. 

It  is  further  interesting  to  note  that  if  current  be  flowing  through 
the  combination  from  the  external  circuit  so  that  a  certain  amount  of 
energy  is  stored  both  in  the  self-induction  and  the  capacity,  on 
suddenly  interrupting  the  external  circuit,  although  the  stored-up 
energy  will  discharge  itself  in  the  closed  loop,  there  will  be  no  differ- 
ence of  potential  between  the  points  a  and  b.  Professor  Gray  has 
pointed  out  an  error  I  have  fallen  into  where,  on  page  668,  I  determine 
the  coefficient  of  self-induction  of  an  alternator  (working  under  certain 
conditions)  by  taking  the  slope  of  the  synchronous  impedance  curve. 

I  have  really  assumed  that  the  equation  V  =  R  C  -f  L  -r-.  still  holds 

for  a  circuit  containing  iron  (and  therefore  with  a  variable  coefficient 
of  self-induction)  provided  we  express  L  in  the  above  equation  as  a 
function  of  C.  Professor  Gray's  criticism  is  quite  justified.  The  true 
equation  should  be — 

V=RC  +  ''M 

o,    V-RC  +  L^jf  +  C^jt 

that  is  to  say,  I  have  left  out  of  account  this  last  term.  As,  however,  I 
have  based  no  calculations  on  this,  the  drift  of  my  argument  is  not 
affected. 

Professor  Carus- Wilson  has  found  fault  with  some  of  my  mathe- 
matics, asking  whether  the  minus  signs  on  page  691  in  the  expres- 
sions for  Vo  should  not  be  positive  signs.  Several  of  the  professors 
have  pointed  out  that  the  mathematics  of  the  subjects  treated  in  my 
paper  have  been  worked  out  before.  It  is  hardly  necessary  for  me  to 
say  that  I  am  perfectly  aware  of  this,  and  have  stated  so  myself  in  the 


1903.]  AND   FIELD:   DISCUSSION.  783 

paper,  and  for  this  reason  I  have  avoided  mathematical  treatment  as  Mr.  Field, 
far  as  possible.  The  theory  of  electric  oscillations  in  capacity  self- 
induction  circuits  was  first  worked  'out  by  Lord  Kelvin  between  fifty 
and  sixty  years  ago.  In  Part  IL  I  have  therefore  merely  stated  the 
general  difiFerential  equation  which  holds  for  such  a  circuit,  and  then 
given  the  particular  solutions  applicable  to  the  cases  experimentally 
investigated.  (I  have,  it  is  true,  as  a  slight  digression,  discussed  briefly 
the  characteristics  of  the  damped  oscillations,  to  remind  those  readers 
unfamiliar  with  the  subject.)  Professor  Carus- Wilson  has  referred  to 
Mr.  C.  P.  Steimnetz's  paper  on  this  subject.  My  attention  was  called 
to  this  after  my  own  was  mostly  written.  Mr.  Steinmetz  in  his 
admirable  work  treats  the  whole  subject  more  as  a  mathematical 
problem.  I  must  say  I  found  the  paper  rather  long  and  difficult,  and 
the  more  important  conclusions  arrived  at  by  making  certain  simpli- 
fications at  the  end  of  the  work,  I  have  tried  to  compass  without  the 
mathematics.  With  regard  to  Part  IIL,  Professor  Carus- Wilson  has 
referred  to  the  work  of  Houston  and  Kennelly.  These,  of  course,  are 
not  the  only  writers  on  this  subject,  e,g.,  C.  P.  Steinmetz,  Bedell,  and 
Crchore,  etc.,  and  I  think  that  the  work  of  even  these  writers  is  to  a 
certain  extent  an  adaptation  of  Fourier  to  electrical  problems  similar 
to  the  heat  problems  treated  mathematically  by  that  physicist.  Being 
again  fully  aware  of  this,  I  have  satisfied  myself  with  stating  merely 
the  general  difiFerential  equations,  and  the  particular  solutions  applic- 
able to  the  case  I  am  considering,  viz.,  resonance  at  the  end  of  a  long 
unloaded  three-phase  cable,  due  to  a  high  order  of  harmonic,  which  I 
have  shown  may  exist  in  a  practicable  alternator,  and  my  intention  has 
been  to  arrive  at  the  conclusion,  by  means  of  a  numerical  result,  as  to 
whether  such  resonance  is  likely  to  prove  dangerous  or  not. 

Coming  now  to  Professor  Carus- Wilson's  query  re  positive  and 
negative  signs,  perhaps  the  best  way  will  be  for  me  to  show  here  how 
the  expressions  in  question  are  arrived  at : — 

The  solutions  given  in  the  paper  for  v  and  c  are  (see  page  689) — 

r  =  V,  [f-^sinCairw/  — aA:-h^)H-c-^"'-'^sin(2irn/  — a(2/  — :r)H-^)] 

c  =  etc. 

a  =  etc (i) 

These  equations  can  of  course  easily  be  verified  by  difiFerentiation. 

We  see  that  when  a:  =  /,  c  =  o,  which  is  the  condition  of  an 
unloaded  cable ;  V,  and  ^  are  arbitrary  constants,  but  if  we  say  that  at 
the  beginning  of  the  cable  we  will  define  the  voltage  as  V©  sin  2  «•  n  /, 
we  can  find  V,  and  ^  as  follows  : — 

Inserting  in{i)  x  =^  0 

VoSin2irn/  =  V,  [sin{2irni  +  ^) -f  €-"'sin(2irn/ —  20/  +  ^)] 
Let  2irii/-f^=so,  then 

VoSin^  =  V,c-"'sin2a/ (2) 

Lct2ir«/-f^  =  -,  then 

VoCos^  =  V,  (I  -h  €-'»'cos2a/) (3) 


784  CONSTABLE   AND    FAWSSETT  [April  23rd, 

Mr.  Field.       Dividing  (2)  by  (3)  we  have 


tan0  =  ^_^_,^, 


_r-'^  sin  2  a  / 

I  +  (-'^^  cos  2a  I 


Squaring  (2)  and  (3),  adding  and  taking  the  square  root,  we  have 

Vo  =  V,  s/r^-  €-•♦-'  +  2  c-'^'  cos  2  a  / (4) 

I  then  state  that  maximum  resonance  will  occur  when  a  /  =  - .  the  rise 

2 

of  voltage  occurring  at  the  free  end  of  the  cable.  Inserting  in  (i)  at  =  /, 
/  =  — ,  we  have  as  the  voltage  at  the  far  end 

2  V,  I  €    2  a  sin  ^2  v« /  +  ^  —  -j  J 
the  maximum  value  of  which  is 

w  a 
2V,€     2    a (5; 

combining  (4)  and  (5),  and  remembering  that  ^  =  tan  0,  we  have  the 

a 

expression 

-  '  tan  »  -  '^  tan  <? 

,— ^-'^l--^-^-_^Vo    or     J'i-l V,.    .    (6) 

^  I   _j_  f-  2  5r  tan  ^  ^  2  e"''  ^^"  ^  I  ^  €~^  tan  0  ^  ' 

These  are  the  expressions  to  which  Professor  Carus- Wilson  objected, 
asking  whether  the  minus  sign  which  I  have  shown  in  thick  type 
should  not  be  positive.  I  would  point  out  that  whether  this  sign  is 
positive  or  negative  entirely  depends  on  the  term  cos  2  a  /  in  (4),  and 

hence  on  the  length  of  the  cable  under  consideration.     Where  /  = 

^  la 

the  case  here  considered  cos  2 a  /  =  —  i,  where  /  =    ,  cos  2a/  =  +  i. 

a 

This  latter  case,  however,  viz.,  where  the  length  of  the  unloaded  cable 

equals  one  half  of  the  wave  length  is  not  a  condition  of  resonance. 

With  the  correct  length  to  give  rise  to  resonance,  the  E.M.F.  at  the 

free  end  will  be  greatest  when  the  copper  resistance  is  smallest.     If  we 

assume   this  becomes  vanishingly  small,  tan  9  =  0,  and  the  voltage 

at  the  free  end  of  the  cable  is  for  /  =  — ,  infinity;  and  for  /  =  -,  Vo; 

2a  "^  a 

that  is,  in  this  case,  the  voltage  at  both  ends  of  the  cable  is  the  same. 

This  hypothetical  case  of  a  length  of  cable  equal  to  one  quarter 
wave  length  where  the  copper  resistance  is  negligible  is  of  great 
interest.  Mr.  Steinmetz  has  pointed  out  that  at  the  one  particular 
frequency  it  behaves  as  a  constant  potential  to  constant-current  trans- 
former, i.e.,  if  constant  potential  be  maintained  at  one  end,  constant 
current  will  be  given  out  at  the  other  irrespective  of  the  nature  of  the 
load  (except,  of  course,  in  the  case  where  the  cable  is  an  open  circuit, 
when  the  potential  rises  to  infinity,  as  above.)  That  this  must  be  so  is 
evident  from  the  equations  for  v  and  c  ;  for  however  the  cable  is  loaded 


1903.]  AND   FIELD:  DISCUSSION.  785 

the  same  form  of  expression  holds  for  the  current  at  one  end  of  the   Mr.  Field 
cable  as  for  the  voltage  at  the  other,  and  vice  versd^  the  coefficients 
only  differing  ;  hence  if  at  one  end  the  voltage  be  maintained  constant, 
at  the  other  end  the  current  will  remain  so,  and  vice  versd:^' 

I  do  not  altogether  agree  with  Professor  Carus- Wilson  in  supposing 
that  this  class  of  resonance  will  never  be  dangerous.  Suppose  an  E.M.F. 
represented  by  the  wave  Curve  XV.  were  applied  to  such  a  cable  as  I 
have  assumed  in  my  calculation,  and  the  13th  harmonic  were  trans- 
formed up  twelve  times.  At  the  far  end  of  the  cable  the  harmonic 
might  quite  easily  be  twice  as  important  as  the  fundamental,  in 
^^hich  case  the  maximum  voltage  would  be  nearly  three  times  that 
of  the  fundamental. 

Messrs.  Constable  and  Fawssett  in  their  excellent  paper  indicate  that 
they  expected  to  find  a  change  of  wave  shape  at  different  points  along 
a  fairly  long  cable,  unloaded,  upon  which  they  experimented,  and 
expressed  surprise  in  failing  to  do  so.  I  think  myself  that  the  length 
of  cable  necessary  before  any  appreciable  change  would  be  observed 
is  far  beyond  anything  they  have  at  Croydon.  I  do  not  think  either 
that  a  change  of  frequency  (within  reason)  would  have  created  the 
expected  variation  as  supposed. 

In  this  connection  I  think  it  will  not  be  altogether  out  of  place  here 
to  ^ve  a  comparatively  simple  graphical  method  for  determining  the 
current  and  voltage  at  any  point  of  a  long  cable  loaded  on  a  more  or 
less  inductive  circuit.  Clearly  we  need  only  consider  one  harmonic  or 
a  sine  function  of  E.M.F.,  for  however  complicated  the  apphed  E.M.F. 
may  be,  each  term  of  the  Fourier's  series  into  which  it  can  be  expanded 
may  be  treated  in  like  manner. 

In  the  first  place  it  is  clear  that  the  solution  given  on  page  689 
becomes  for  a  loaded  cable 


T»  =  W**  sin  (2  x« /  — a;rH-0') +  V"€-*^^'-'>sin  (2  Tw/  —  a(2/  —  :r)  + ^") 

V" 
+  0)-—. 

r 


c=:— f-*'  sin  (2  7r/j/  —  a^r-l-^'  +  0) f-=»r»/-'^  sin(2x;i/  —  0(2/  —  x) 


where 

I  2'jrnK 

=      ,_  or 


V    2  TT  W    ^ 


•  In  this  connection  my  brother,  A.  B.  Field,  has  pointed  out  that  the 
following  combination  of  self-inductions  and  capacity  acts  as  a  constant 
potential  to  current  transformer,  provided  it  is  loaded  on  a  non-inductive  load, 

and  n  is  such  that  2  7rw  =  v  f-rv  ;  the  proof  is  simple  ;  the  combination  is 
^    1^  K. 

very  interesting.    I  understand  that  Mr.  Steinmetz  first  called  attention  to  this 

combination. 


Fig.  X. 


786 


CONSTABLE  AND   FAWSSETT 


[April  23rd» 


Mr.  Fidd.      and  whcrc  V,  V",  \l/',  yjf"  arc  determined  by  the  terminal  conditions— 


X  ss:  Of  V  ssVo  sin  2  nnt;  jr  =  /,  c  = 


Vi 


('+'!,) 


v/  being  the  value  of  v,  obtained  by  putting  in  the  value  a:  =  /,  and  r 
and  /  are  the  resistance  and  coefficient  of  self-induction  of  the  circuit 
external  to  the  cable,  hereafter  termed  "the  external  circuit."  Let  the 
impedance  of  this  circuit  or  Jr'  +  4ir'n'/'  be  denoted  by  T.  We  see 
that  V  and  c  consist  each  of  an  original  and  a  reflected  wave,  and  that 
the  phase  of  each  wave  at  any  particular  instant  changes  uniformly  as 
we  go  along  the  cable.  The  difference  of  phase  at  two  points  separated 
by  the  distance  a;  is  w  where  ut  s=  ax,  whereas  the  ratio  of  the  ampli- 
tudes at  these  points  is  c-  tan  #  if^  now,  we  draw  a  logarithmic  spiral, 
r  ^=  c«tan(?(see  Fig.  Y),  of  which  the  co-ordinates  are  r  and  w,  and 

say  that  the  radius  O  a  represents 
in  magnitude  and  phase  the  original 
wave  at  the  far  end  of  the  cable, 
then  O^  will  represent  the  magni- 
tude and  phase  at  a  distance  x,  from 
the  end,  where  w,  =  «*i.  Similarly 
if  O  a'  represent  the  reflected  wave 
at  the  end  of  the  cable,  Ob'  will 
again  be  the  phase  and  magnitude 
of  the  same  at  distance  x^  from  end. 
The  conditions  which  obtain  at  the 
end  of  the  cable  are  these  :  Let  O  V, 
Fig.  Z,  be  the  voltage,  and  O  c  the 
current.  I  have  shown  these  in  two 
distinct  diagrams  for  the  sake  of 
clearness,  preferably  they  should  be  combined  in  one.  O  c  =  O  V/I' 
and  cos  %  is  the  power  factor  of  the  circuit  supplied  by  the  cable.  Now 
O  V  is  the  resultant  of  two  waves,  say  O  ti  and  O  e  ;  corresponding  to 
each  of  these  is  a  current  wave,  of  which  the  amplitudes  are  O  dly,  O  e/y, 
and  each  is  in  advance  of  the  corresponding  potential  wave  by  the 
angle  0.  The  resultant  oi  O  d  and  O  ^  is  O  V,  while  the  difference  of 
the  two  corresponding  current  waves  is  O  C.  This  is  evident  from  the 
form  of  the  equations  v  and  c. 

Draw  a  line  O  P,  set  back  from  O  c  by  the  angle  0.    Bisect  O  V  and 

draw  through  the  centre  a  line  parallel  to  O  P  of  length  O  V .  J'j,  so  that 

this  vector  is  in  its  turn  bisected  by  O  V.  Complete  the  parallelogram, 
of  which  these  vectors  are  the  diagonals,  then  Od,  Oe,  represent  the 
two  voltage  waves,  because  they  give  a  resultant  OV,  and  when  we 
draw  in  the  corresponding  current  waves  in  the  current  diagram,  or 
O  d\  O  e',  these  are  such  that  (by  construction)  O  rf'  —  O  <?'  =  Oc. 

We  have  now  only  to  superimpose  the  logarithmic  spiral  on  the  top 
of  each  diagram,  rotate  O  rf,  O  ^  forwards  through  the  angle  J  (=z  at) 
and  O  ^,  O  ^r'  backwards  through  the  same  angle,  increasing  or  decreasing 
the  magnitudes  of  these  vectors  in  proportion  to  the  value  of  the  polar 


Fig.  Y. 


1903.] 


AND  FIELD:   DISCUSSION. 


787 


co-ordinate  of  the  spiral,  to  find  the  values  of  the  original  and  reflected   Mr.  Field 
voltage  and  current  waves  at  the  beginning  of  the  cable.    Taking  the 
resultant  of  the  two  voltage  vectors  and  equating  this  to  Vo sin  2  irn  / 
we  fix  the  scale  of  the  diagram,  and  the  datum  from  which  time  is 

measured.  For  example,  suppose  al=     we  rotate  O  d  forward  through 

a  right  angle  and  increase  it  in  the  proportion  O  s'  :  O  s,  we  rotate  O  e 
backwards  through  a  right  angle  ancl  decrease  it  in  the  proportion 
O  t  :  Ot,  These  two  vectors  represent  the  magnitude  and  phase  of  the 
original  and  reflected  waves  at  the  beginning  of  the  cable.  Their 
resultant  is  O  Vq.  Since  the  applied  E.M.F.  is  Vo  sin  2  x  n  /  the  length 
OVo  represents  the  voltage  Vo  which  fixes  the  scale  of  the  diagram, 
while  all  phase  relations  of  currents,  voltages,  etc.,  are  referable  to 
O  Vo.  It  is  thus  clear  that  by  determining  the  values  of  the  original 
and  reflected  waves  and  taking  the  sum  or  difference  as  the  case  may  be, 
the  true  value  of  voltage  and  current  at  any  point  of  the  cable  may  be 
determined. 


Fk;.  Z. 


Professor  Carus- Wilson  asked  for  a  further  explanation  of  the  footnote 
on  page  688.  I  thought  this  was  sufficiently  clear.  pXx  of  Part  III. 
have  entirely  different  dimensions  from  RLK  in  II.  The  latter  are 
resistance,  self-induction,  and  capacity  respectively,  the  former  are 
the  same  physical  quantities  divided  by  a  length,  or  resistance,  self- 
induction,  etc.,  per  unit  length.    In  Part  II.  v  ,-j^  is  a  frequency,  or  of 

the  dimensions  of  T-' :   in  Part  III.  \/ ^-^  is  a  velocity  or    -7"-     : 

^  XK  ^  time 

it  was  to  keep  this  distinction  clearly  before  us  that  I  resorted  to  the 
Greek  letters  in  Part  III. 

I  do  not  agree  with  Professor  Carus- Wilson  in  his  remarks  re  the  mis- 
application of  the  term  resonance,  nor  do  I  think  that  Houston  and 

Kennelly  were  the  originators  of  the  term.  Resonance  was  known  and 
understood  in  other  branches  of  physics,  vide  Helmholtz's  Resonators 
(accoustic),  long  before  Houston  and  Kennelly's  paper.    One  may  say 


788  CONSTABLE  AND   FAWSSETT  [April  23rd. 

Mr.  Field.  that  the  best  definition  ol  resonance  is  "  Synchronism  between  the 
natural  and  forced  vibrations  of  a  system."  With  this  definition  the 
phenomena  investigated  in  Part  I.  are  true  resonance  effects.  We  are 
dealing  with  combinations  of  capacity  and  self-induction  which  have 
a  definite  periodic  time  of  their  own  (natural  vibrations),  if  now  the 
frequency  of  the  supply  (or  forced  vibrations)  correspond  with  the 
natural,  we  get  serious  magnification  of  the  amplitude  of  the  vibration 
or  resonance.  As  another  example,  the  periodic  time  of  the  vibrating 
portion  of  the  oscillograph  is  say,  Ttriwath  of  a  second,  suppose  we 
passed  an  oscillatory  current  of  the  same  frequency  through  the  strips 
we  should  have  a  case  of  mechanical  resonance,  the  amplitude  of 
vibration  being  largely  in  excess  of  that  which  would  normally  cor- 
respond to  the  current  flowing.  This  is  resonance  in  the  strictest  sense, 
and  Professor  Carus-Wilson  is  unduly  limiting  the  use  of  the  expression  in 
restricting  it  only  to  such  phenomena  as  are  dealt  with  in  Part  III.  In 
Part  II.  I  grant  it  is  hardly  in  order  to  apply  the  term  "  resonance  "  to 
the  phenomena  discussed,  as  there  we  are  only  dealing  with  the  natural 
vibrations,  but  I  have  pointed  out  on  page  682  that  while  in  Part  I.  we 
have  been  dealing  with  cases  wherein  the  frequency  of  the  supply 
synchronised  with  the   natural  oscillations  (or  frequency  of  supply 

=  -— V^:p^),  in    Part    II.    we    are  dealing  only  with    the    natural 

oscillation,  the  frequency  of   which  is  the  same  as  the  above,  viz., 

—   ^  |-^.    We  may  almost  consider  the  latter  case  as  a  particular 

instance  of  the  former,  where  the  amplitude  of  forced  oscillation  is 
zero.  At  any  rate,  the  laws  governing  the  two  cases  are  so  similar 
that  I  have  classed  the  latter,  though  possibly  incorrectly,  as  a 
resonance  effect. 

Professor  Maclean  (Glasgow)  has  contributed  some  very  interesting 
remarks  re  harmonics  present  in  some  of  the  wave  forms  I  have 
reproduced.  It  is  quite  evident  that  in  a  three-phase  Y  connected 
generator  the  3rd,  6th,  9th,  etc.,  harmonics  can  have  no  existence.* 
If,  however,  the  voltage  wave  between  one  terminal  and  the  neutral 
point  had  been  reproduced  (Le,,  of  one  leg  of  the  winding  only)  I  fully 
believe  that  traces  of  the  3rd,  9th,  15th,  etc.,  would  have  been  found. 

I  have  pointed  out  that  in  such  a  generator  the  only  harmonics 
which  can  exist  (voltage  being  taken  between  two  line  wires)  are  given 
by  the  expression  6  w  ^i  i,  where  n  is  any  whole  number.  If  we  give  n 
a  value  equal  to  the  number  of  slots  per  pole  per  phase  we  get  the  two 
harmonics,  which  will  in  all  probability  be  the  most  predominant.  In 
the  curves  under  examination  we  should  expect  to  find  only  the  5th, 
7th,  nth,  13th,  17th,  19th,  etc.  Similarly  with  regard  to  the  ripple  in 
the  rotary  D.C.  E.M.F.,  as  Mr.  Hird  has  pointed  out,  the  5th  and  7th 
will  produce  a  ripple  of  six  times  the  normal  frequency,  the  nth  and 
13th  of  twelve  times,  and  so  on ;  hence  the  order  of  ripples  will  always 
be  a  multiple  of  six. 

•  I  have  to  thank  Dr.  J.  B.  Henderson  of  Glasf^ow  University  for  first 
calling  my  attention  to  the  fact  that  on  theoretical  grounds  these  harmonics 
must  be  non-existent  in  the  alternators  under  discussion. 


1903.]  AND   FIELD:   DISCUSSION.  789 

It  is  to  be  observed  that  since  the  nth  and  13th  harmonics  will  Mr.  Field. 
both  produce  a  ripple  in  the  D.C.  E.M.F.  of  the  rotary  of  twelve 
times  the  normal  frequency,  these  may  either  neutralise  or  aug- 
ment each  other.  The  cases  are  therefore  possible  that  a  large 
ripple  may  appear  !h  the  D.C.  E.M.F.  due  to  relatively  small 
harmonics  in  the  A.C.  wave,  or  again,  a  perfectly  straight  D.C. 
E.M.F.  line  may  result  from  an  A.C.  E.M.F.  wave  having  consider- 
able harmonics.  The  same  thing  of  course  applies  to  the  other 
pairs  of  harmonics.  Professor  Maclean  has  drawn  attention  to  the 
existence  of  a  considerable  5th  harmonic  in  certain  wave  forms. 
The  somewhat  rough  and  ready  explanation  I  have  given  on  page  657 
of  the  cause  of  the  existence  of  the  nth  and  13th  harmonics  is  based 
entirely  on  the  number  of  teeth  in  the  armature.  I  point  out  that  there 
are  twelve  teeth  per  period,  therefore  we  might  expect  twelve  irregu- 
larities in  the  magnetic  curve,  hence  the  reason  for  considering  the 
magnetic  curve  represented  by  F  N  sin  Jfe  /  -f  a  (i  —  cos  12  ife  /),  etc. ; 
following  out  the  argument  of  the  paper  it  would  of  course  have 
been  incorrect  to  assume  an  expression  such  as  a  (i  —  cos  6kt)  as 
Professor  Maclean  indicates.  On  the  other  hand,  the  existence  of  a  pro- 
nounced 5th  harmonic  may  very  readily  be  imagined  as  due  to  the 
crowding  together  of  the  copper  in  the  armature.  It  is  quite  con- 
ceivable that  if  the  machine  were  a  smpoth-core  alternator,  but  with 
the  copper  crowded  together  in  the  same  way  as  in  the  actual  case,  a 
5th  harmonic  might  be  the  result.  It  is  to  be  regretted  that  Professor 
Maclean  had  not  time  to  continue  his  analysis  of  the  curves  published 
and  determine  in  what  proportion  the  13th  was  present. 

Coming  now  to  Mr.  Duddell's  remarks,  I  would  say  in  the  first  place 
that  I  am  quite  aware  of  his  beautiful  photographic  contrivance  for 
obtaining  a  continuous  record  from  the  oscillograph,  but  I  could  not 
use  it  on  the  score  of  expense.  The  makers  quoted  me  something  like 
£^0  for  the  apparatus,  and  I  understand  that  it  is  a  comparatively  easy 
matter  to  reel  off  £xo  or  ;£i2  worth  of  films  in  a  few  minutes. 

I  therefore  resorted  to  the  dark  slide  shown  in  the  paper ;  these 
cost  me  about  30s.  a  piece  and  id.  per  exposure.  Of  course,  I  was 
dealing  with  periodic  effects,  and  those  effects  which  were  not  really 
periodic  I  made  periodic  by  employing  the  contact  maker  already 
described.  I  consider  I  obtained  excellent  results  with  my  dark  slides, 
and  I  can  strongly  recommend  the  use  of  the  same  for  similar  work. 
Where,  however,  it  is  desired  to  study  such  effects  as  those  when  arcs 
break  out,  etc.,  I  admit  there  is  no  way  of  doing  it  satisfactorily  except 
by  the  very  expensive  continuous  film  device. 

Mr.  Duddell  referred  to  the  effect  on  the  A.C.  voltage  of  a  rotary, 
of  sparking  at  the  commutator,  and  stated  that  he  would  not  like  to  say 
what  might  happen  on  account  of  resonance  on  the  A.C.  side  should 
this  sparking  become  bad.  I  have  myself  observed  similar  effects  pro- 
duced by  sparking,  not  on  a  rotary,  but  at  the  contact  breaker  already 
referred  to.  I  do  not  think,  however,  that  this  is  likely  to  give  rise  to 
dangerous  oscillations  in  the  cable  system.  It  appears  to  me  that  there 
is  just  as  much  likelihood  of  such  effects  occurring  on  the  D.C.  side  as 
the  A.C.,  and  if  they  are  serious,  some  such  effect  would  have  been 


790  CONSTABLE  AND   FAWSSETT  [April  23rd, 

Mr.  Field.  noticed  and  recorded  before  this  in  connection  with  sparky  D.C. 
generators  which  supply  considerable  cable  networks.  In  the  paper, 
however,  I  have  called  attention  to  the  possibility  of  resonance 
with  D.C.  machines  due  to  slight  periodic  voltage  fluctuations 
corresponding  to  the  number  of  armature  slots  or  commutator  seg- 
ments, e,g.j  compare  ripples  on  Curve  IV. ;  and  although  resonance 
under  these  circumstances  would  not  probably  assume  any  very  great 
dimensions  I  think  that  in  the  case  of  rotary  converters  the  e£Fect  due 
to  the  accentuated  ripples  in  the  D.C.  voltage  illustrated  in  the  paper 
might  become  very  serious. 

Attention  has  been  drawn  by  several  speakers  to  the  danger  in 
running  up  a  generator  to  full  speed,  when  already  excited  and  con- 
nected to  a  cable  system.  This  is  a  point  I  attach  considerable 
importance  to  and  have  dealt  with  myself  in  the  paper.  We  did 
not  appreciate  the  fact  at  first  at  all  at  Glasgow,  but  nevertheless 
noticed  a  curious  effect  during  the  process  of  starting  up  and  shut- 
ting down.  At  a  certain  speed  or  speeds,  as  mentioned  by  my  former 
assistant,  Mr.  S.  Blackley,  a  kind  of  static  sparking  was  observable 
between  the  live  metal  portions  of  the  Westinghouse  high-tension 
breakers  into  the  wooden  arms  on  which  they  were  carried.  It  was 
afterwards  found  that  these  eflFects  corresponded  with  the  critical 
speeds  at  which  partial  resonance  occurred. 

Mr.  Duddell  referred  at  some  length  to  the  form  factor  ;  he 
attaches  very  great  importance  to  the  strain  put  upon  the  system  due 
to  a  high  form  factor.  In  my  paper  I  have  said  it  is  a  mistake  to  attach 
too  much  importance  to  these  eflFects,  and  to  get  frightened  at  them, 
though  I  most  strongly  urge  the  advisability  of  every  engineer  investi- 
gating fully  what  is  going  on  inside  his  system  so  that  he  is  in  a  position 
to  appreciate  and  overcome  any  difl&culties  which  may  be  introduced 
thereby.  I  may  say,  however,  that  at  Glasgow,  with  the  exception  of 
the  one  isolated  case  above  mentioned,  there  was  nothing  to  indicate 
that  anything  abnormal  was  occurring  at  aU.  It  was  only  because  I 
expected  to  find  deformations  of  wave  shape  from  theoretical  consider- 
ations that  I  was  led  to  search  for  the  results  here  published,  and  I  may 
say  that  in  some  instances  a  very  considerable  amount  of  experimenting 
was  necessary  before  I  found  the  critical  conditions. 

When  I  was  recently  in  the  States  I  made  a  special  point  of  asking 
central  station  engineers  whether  they  experienced  difl&culties  in  work- 
ing from  these  causes,  and  the  almost  invariable  answer  I  received  was 
that  but  for  the  theoretical  writings  of  certain  authors  they  would  not 
know  that  such  phenomena  as  resonance  existed  at  all.  Of  course  I 
know  that  certain  stations  over  here  have  had  considerable  trouble  with 
cables  and  apparatus,  but  nevertheless  I  am  inclined  to  think  that  with 
modern  up-to-date  systems  of  cables  and  apparatus  there  is  not  much 
to  fear.  As  regards  form  factor,  even  with  a  very  distorted  wave  such 
as  Curve  XV.,  it  does  not  exceed  2  or  2*2,  whereas  the  form  factor  of  a 
sine- wave  is  1*4,  i.e.,  the  maximum  E.M.F.  in  the  former  case  is  only 
about  50  per  cent,  greater  than  in  the  latter,  and  if  the  insulation  of  the 
system  won't  stand  this  the  sooner  it  breaks  down  and  is  taken  out  the 
better. 


1903.]  AND   FIELD:  DISCUSSION,  791 

Another  reason  why  I  urge  that  too  much  importance  should  not  be  Mr.  Field, 
attached  to  the  form  factor  is  this  :  At  the  last  meeting  I  indicated  that 
unless  very  excessive  voltages  be  applied  there  is  strong  probability  that 
the  determining  factor  as  to  whether  an  insulating  material  will  break 
down  or  not  is  the  heat  developed  per  unit  volume  and  the  actual 
deterioration  of  the  material  thereby  caused.  If  this  be  so,  it  is  the 
R.M.S.  of  the  voltage  wave  we  have  to  consider  and  not  the  form 
factor.  I  do  not  wish  to  be  misunderstood  here ;  if  it  is  a  question  of 
the  insulation  breaking  down  due  to  sparking  across  some  air-gap  or  the 
like,  I  do  not  dispute  that  it  is  the  form  factor  we  have  to  look  to,  but 
what  I  mean  is,  if  we  consider  a  moderate  excess  of  voltage  which  will 
not  instantly  break  down  the  insulation,  but  after,  say,  5  or  lo  minutes, 
or  even  half  an  hour,  then  the  primary  cause  of  breakdown  will  pro- 
bably be  due  to  excessive  local  heating  at  the  weakest  spot,  and  in  such 
a  case  a  partial  resonance  producing  a  greater  form  factor  is  not  serious 
provided  it  does  not  increase  the  R.M.S.  value.  I  say  this  with  con- 
siderable diffidence,  and  I'm  afraid  Mr.  Duddell  will  not  agree  with  me. 
I  only  wish  that  Mr.  Duddell  had  written  a  paper  on  this  subject  instead 
of  myself  ;  he  has  made  a  large  number  of  experiments  and  has  a  fund 
of  information  which  ought  lo  be  published  for  the  benefit  of  the  electri- 
cal industry ;  I  hope  he  will,  in  communicating  his  remarks  to  the 
Journal,  expand  them  considerably  and  give  us  further  details  of  his 
careful  study  of  this  most  important  subject. 

Major  Cardew  suggested  that  the  assumptions  made  in  the  paper  as 
to  the  suddenness  with  which  a  circuit  is  made  or  broken  are  untenable. 
He  suggested  that  the  switch  itself  had  a  certain  variable  amount  of 
capacity  which  was  really  in  series  with  the  capacity  of  the  cable,  and 
on  closing  the  switch  this  capacity  was  gradually  reduced,  thus  gradually 
raising  the  potential  of  the  cable  before  the  circuit  is  actually  closed. 
Now  if  we  take  the  capacity  of  a  "aD"  cable,  we  find  that  it  is  about 
equivalent  to  that  of  two  plates  750  sq.  ft.  area,  or  28  feet  square, 
separated  by,  say,  i".  What  can  the  capacity  of  the  metal  parts  of  the 
switch  be  in  comparison  with  this  ?  Probably  not  more  than  -njJinjth 
part  until  the  contacts  came  within  striking  distance,  then  a  spark 
passes  and  the  insulation  of  the  air-gap  being  totally  broken  down,  the 
circuit  may  be  said  to  be  closed  instantly.  Again,  on  opening  a  circuit 
Major  Cardew  suggested  that  the  air  arc  which  is  formed  and  gradually 
lengthened  causes  the  current  to  gradually  die  down.  Now  experi- 
ments show  that  this  is  very  far  from  being  the  case.  A  high-tension 
air  arc  seems  to  finally  extinguish  itself  with  what  might  almost  be 
termed  explosive  suddenness,  even  though  it  may  have  lasted  several 
seconds  previously.  Whatever  be  the  reason  it  has  now  been  estab- 
lished beyond  the  region  of  doubt  that  the  high-tension  air  arc  is  about 
the  most  vicious  phenomenon  possible  in  setting  up  high  potential 
oscillations  in  the  circuit.  I  admit  that  one  would  nalurally  expect  the 
air  arc  to  be  equivalent  to  a  gradual,  and  an  arc  under  oil  to  an  abrupt 
opening  of  the  circuit.  Oscillograph  experiments  show  just  the  reverse. 
If  a  circuit  be  broken  under  oil  there  will  be  no  high  potential  oscil- 
lations called  into  existence.  As  Professor  Carus- Wilson  has  pointed 
out,  this  is  of  the  greatest  moment  to  engineers  who  have  to  deal  with 
Vol.  82.  62 


792  CONSTABLE,   FAWSSETT  AND  FIELD.        [April  28rd, 

Mr.  Field,  high-voltage  machinery.  The  correctness  of  the  above  statements  is 
beyond  dispute,  having  been  Qstablished  by  numerous  experiments  both 
in  this  country  and  in  the  States.  It  shows  us  at  once  that  all  apparatus 
such  as  switches,  fuses,  etc.,  where  an  arc  can  possibly  form  in  air  most 
be  avoided  in  high-tension  circuits,  whereas  oil  switches  and  oil  fuses 
may  be  used  not  only  with  certainty  but  without  engendering  the  danger 
of  high  potential  rises.  I  now  wish  to  touch  upon  the  matter  of  charging 
gear  for  cable  networks.  A  good  deal  of  correspondence  has  taken 
place  in  the  electrical  papers  lately  on  this  subject.  It  seems  to  have 
been  the  experience  of  some  stations  in  this  country  that  a  main- 
charging  gear  is  necessary.  It  is  noteworthy  that  in  the  States  I 
did  not  come  across  a  single  instance  where  one  was  installed.  However, 
I  would  say,  that  if  any  engineer  wishes  one,  let  him  have  it  by  all 
means,  but  let  it  take  the  form  of  an  absolutely  non-inductive  resistance. 
For  this  purpose  a  water  resistance  is  manifestly  correct.  Anything  in 
the  nature  of  self-inductions,  transformers,  and  the  like,  should  be 
discarded  as  highly  dangerous.  Mr.  Partridge  has  lately  described  an 
arrangement  used  at  Deptford  consisting  of  a  transformer,  the  high- 
tension  side  of  which  is  placed  in  series  with  the  cable,  and  the  low- 
tension  side  gradually  short-circuited  through  a  water  resistance.  This 
has  apparently  given  satisfaction,  and  all  I  would  say  about  it  is,  that 
Deptford  has  been  very  fortunate.  The  t)rpe  of  gear  is  certainly  risky, 
at  certain  instants  it  introduces  practically  a  pure  self-induction  in  series 
with  the  capacity.  It  would  appear  that  the  values  are  such  that  the 
combination  does  not  happen  to  be  a  dangerous  one.  We  must 
remember  that  the  Deptford  wave  form  is  a  very  nearly  true  sine-wave 
without  ripples.  If  a  number  of  different  harmonics  existed  of  any 
appreciable  amplitude,  it  is  clear  that  with  the  possible  variations  of 
capacity,  self-induction,  and  slight  variations  of  speed,  resonance  with 
one  or  other  of  the  harmonics  would  be  very  likely  to  occur  before 
long.  Water  resistance  mains-charging  gear  can  be  made,  in  fact  is 
made,  entirely  reliable,  simple  in  operation,  comparatively  inexpensive, 
and  by  proper  construction  the  insulation  can  be  made  as  high  as 
necessary.  It  is  in  fact  thoroughly  practicable,  both  mechanically  and 
electrically. 

With  regard  to  applying  high-voltage  tests  to  cables,  in  my 
opinion  a  mediumly  severe  test  for  a  long  period,  say  30  minutes,  is 
preferable  to  a  much  higher  voltage  applied  for  only  a  few  seconds. 
If  a  cable  will  stand  a  test  for  30  minutes,  it  is  very  unlikely  that 
it  will  be  permanently  damaged  by  the  strain  put  upon  it.  If,  how- 
ever, a  very  high  voltage  be  applied  for  five  seconds,  it  is  possible 
permanent  damage  may  be  done  without  actually  breaking  down  the 
cable.  It  may  stand  for  five  seconds,  but  break  down  after  ten.  This 
means  that  deterioration  is  going  on  at  some  spot  in  the  cable  during 
those  ten  seconds,  and  consequently  considerable  deterioration  (pro- 
bably scorching  as  explained  theretofore)  may  have  already  taken  place 
at  some  spots  during  the  first  five  seconds. 

Mr.  Atchison's  communicated  remarks  are  of  great  interest.  .1  pre- 
sirnie  the  alternator  used  was  a  comparatively  small  one  ;  I  should 
judge   somewhere  in  the  neighbourhood  of  5  kilowatts.      Resonance 


1903.]  ELECTIONS.  793 

with  the  fifth  harmonic  required  27  m.f .  capacity — this  bears  out  the  Mr.  Field 
contention  of  the  paper  that  under  ordinary  central  station  conditions 
resonance  with  low  harmonics  are  not  likely  to  occur,  but  only  with  the 
higher  ones.  I  wish  to  thank  Dr.  Thornton  and  Professor  Hay  for  the 
references  they  have  given  to  previous  experimental  work  on  the 
subjects  treated  in  this  paper. 

Mr.  W.  B.  Hird's  remarks  have  already  been  answered  in  this 
reply.  I  wish  further  to  thank  Dr.  Henderson  for  the  table  he  has 
worked  out  and  appended,  and  lastly,  to  express  my  appreciation 
of  the  generous  manner  in  which  my  paper  has  been  received  and 
discDssed  both  in  Glasgow  and  London. 

The  President  :  Gentlemen,  I  ask  you  to  accord  a  most  hearty  vote  The 
of  thanks  to  the  authors  for  their  papers.     I  am  sure  they  have  been 
most  interesting  in  every  way,  while  the  discussion  we  h^ve  had  has 
been  particularly  instructive,  and  really  shows  the  value  of  the  papers. 
The  vote  was  carried  by  acclamation. 

The  President  reported  that  the  scrutineers  announced  that  the 
following  candidates  had  been  duly  elected : — 

As  Members. 
Charles  Orme  Bastian.  |       Henry  Sherman  Loud. 

As  Associate  Members. 


President. 


Joseph  John  Perkins  Barker. 
Hermann  Bohle. 
Frank  William  Davis. 
John  Walter  Henry  Hawes. 
Alexander  Percy  MacAlister. 


James  Geo.  McLean. 
James  Mitchell-Cocks. 
Thomas  Penrose. 
Philip  Sydney  Saunderson. 
John  Vincent. 


Josiah  Mower  Wallwin. 

As  Associates, 
Edward  Coveney.  |       John  H.  Pennefeather. 

As  Students, 


Hubert  Henry  Andrews. 
Isaac  Henry  Becker. 
Randal  Eugene  Golden. 


Frederick  William  Halford. 
Richard  Pentony. 
Kenneth  John  Thomson. 


794         TRANSFERS,  DONATIONS  TO  LIBRARY,   ETC.     [April  30tti, 

The  Three  Hundred  and  Ninety-third  Ordinai7  General 
Meeting  of  the  Institution  was  held  at  the  Institution  of 
Civil  Engineers,  Great  George  Street,  Westminster,  on 
Thursday,  April  30th,  1903— Mr.  Robert  K.  Gray, 
President,  in  the  chair. 

The  Minutes  of  the  Ordinary  General  Meeting  held  on  April  23, 
1903,  were  read  and  confirmed. 

The  names  of  new  candidates  for  election  into  the  Institution  were 
taken  as  read,  and  it  was  ordered  that  their  names  should  be  suspended 
in  the  Library. 

The  following  list  of  transfers  was  published  as  having  been  approved 
by  the  Council : — 

From  the  class  of  Associate  Members  to  that  of  Members — 

Randell  Howard  Fletcher.        I      Gerald  Hart  Jackson. 
John  H.  C.  Hewett.  I       Herbert  William  David  Lewis. 

Julius  Leonard  Fox  Vogel. 

From  the  class  of  Associates  to  that  of  Associate  Members — 

John  Daniel  Dyson.  |         William  Fennell. 

Francis  William  Hewitt. 

From  the  class  of  Students  to  that  of  Associate  Members — 
Francis  Powell  Williams. 

From  the  class  of  Students  to  that  of  Associates — 
Arthur  Blok. 

Messrs.  R.  B.  Hungerford  and  C.  J.  Phillips  were  appointed  scruti- 
neers of  the  ballot  for  the  election  of  new  members. 

Donations  to  the  Library  were  announced  as  having  been  received 
from  the  Museo  Civico,  Como,  and  Mr.  D.  S.  Munro ;  and  to  the 
Building  Fund  from  Messrs.  J.  Grant  and  H.  Owen,  to  whom  the  thanks 
of  the  meeting  were  duly  accorded. 

The  Chairman  :  With  reference  to  these  donations,  I  may  mention 
that  the  first  is  from  the  Museo  Civico,  of  Como,  who  have  sent  for  our 
Library  a  copy  of  a  volume,  with  an  illuminated  cover,  connected  with 
what  has  been  done  by  Volta.  They  also  sent  us  eight  copies  for 
distribution  at  our  discretion  amongst  various  Libraries,  and  to-day  the 
Council  decided  what  should  be  done  in  distributing  these.  I  mention 
this  gift  specially  because  it  comes  from  a  rather  important  body,  and 
is  a  token  of  their  regard  for  the  members  of  the  Institution  who 
recently  visited  Ital}'. 

I  have  to  announce  that  the  annual  conversazione  will  take  place  on 
Tuesday,  June  23rd,  at  the  Natural  History  Museum,  and  that  on  June 
nth  a  concert  will  be  given.    These  dates  have  been  selected  because 


1903.]  AITKEN:   DIVIDED   A^ULTIPLE   SWITCHBOARDS:        795 

there  will  be  in  London  in  June  the  Delegates  of  the  International 
Telegraph  Conference,  and  it  was  thought  by  your  Council  that  it 
would  be  proper  to  give  these  gentlemen  an  opportunity  of  being 
present  at  the  entertainments. 

In  front  of  me  you  will  notice  the  shield  which  has  been  subscribed 
for  by  our  students,  and  which  is  destined  to  be  placed  on  the  tomb  of 
Volta  at  Camnago.  I  feel  certain  the  members  present  will  Hke  to 
examine  it ;  it  is  a  work  of  art,  and  was  designed  for  the  students  by 
Mr.  Gilbert  Bayes,  a  former  art  student  at  the  Finsbury  Technical 
College,  a  Gold  Medalist  of  the  Royal  Academy  School,  and  now 
instructor  in  modelling  at  Finsbury.  I  may  remind  you  that  a  replica 
of  this  shield  was  deposited  in  the  Volta  Mausoleum,  Camnago,  by  Mr. 
Hewitt,  who  represented  our  students.  When  the  shield  is  affixed  to 
Volta's  tomb,  the  Museum  of  Como  will  be  asked  to  receive  the  cast, 
which  is  now  at  Camnago.  Within  the  next  few  days  the  shield 
will  be  forwarded  to  its  destination. 

The  following  paper  was  then  read  : — 


DIVIDED    MULTIPLE    SWITCHBOARDS:    AN    EF- 
FICIENT   TELEPHONE     SYSTEM     FOR    THE      L^ 
WORLD'S  CAPITALS. 

By   W.  AiTKEN,  Member. 

The  designing  of  an  efficient  telephone  system  for  one  of  the  great 
centres  of  industry  requires  much  careful  consideration,  as  the  subject 
bristles  with  difficulties.  The  problem,  however,  is  a  most  interesting 
one.  Any  system  proposed  must  be  as  simple  as  possible,  consistent 
with  efficiency — quick,  direct,  reliable. 

Before  putting  my  suggestions  before  you  it  will  be  advisable 
to  consider  briefly  the  methods  that  have  already  been  put  forward. 

The  general  practice  has  been  to  divide  the  area  to  be  telephoned 
into  sections,  to  place  in  each  section  an  exchange,  to  connect  the 
various  exchanges  together  by  direct  junction  wires  where  the  traffic  is 
considerable,  and  to  connect  the  various  exchanges  or  groups  of 
exchanges  also  to  one  or  more  junction  centrals,  through  which 
connections  are  obtained  to  small  exchanges  where  the  traffic  is  not 
sufficient  to  warrant  direct  junctions  being  run,  so  that  complete 
intercommunication  may  be  established.  Figure  i  shows  such  an 
arrangement. 

The  weak  spot  of  such  a  system  is  the  multiplicity  of  junction 
calls.  Only  a  small  proportion  of  the  total  calls  can  be  dealt  with 
direct  by  one  operator.  In  the  larger  exchanges  50  per  cent,  of 
the  calls  may  be  local,  but  in  the  majority  of  cases  the  percentage 
will  be  much  smaller,  in  some  cases  only  5  or  10  per  cent.  Fifty 
to  95  per  cent,  of  the  calls  have,  therefore,  to  be  handled  by 
two — in  some  cases  three— operators.  The  service  is  not,  therefore, 
ideal.  The  call  has  to  be  passed  from  exchange  to  exchange,  and  a 
junction  call   takes  about  twice  as  long  to  complete  as  a  iQcal  one, 


796    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 


1908.] 


AN  EFFICIENT  TELEPHONE  SYSTEM. 


797 


The  subscriber's  number  has  to  be  received  by  more  than  one 
operator.  There  is  also  the  possibility  of  delay  and  inefficient  trans- 
mission because  of  the  compHcations  of  the  junction  circuits  and  their 
consequent  liability  to  go  out  of  order.  In  practice  it  is  found  that  for  an 
efficient  service  where  there  are  a  considerable  number  of  exchanges, 
for  every  loo  subscribers'  lines  twenty  junction  lines  are  required, 
ID  per  cent,  for  incoming  work  and  lo  per  cent,  for  outgoing  work. 
In  addition  the  junction  circuit  is. much  more  complicated  than  a 
subscriber's  circuit  ;  its  apparatus  is  more  intricate  and  requires 
more  expert  handling. 

What  is  recognised  as  the  best  method  of  working  junction  lines, 
and  used  by  the  National  Telephone  Company,  is  as  follows  : — 
At  the  outgoing  end  the  lines  are  multipled  three  times  on  every 
two  sections,  so  that  every  operator  has  every  line  almost  directly 
in  front  of  her.  At  the  incoming  end  the  junctions  are  arranged 
in  groups  of  25  (average  number)  per  operator  and  end  in  plugs^  only 


Fig.  2. 


signalling  apparatus  being  in  addition.  A  service  or  order  wire  is 
provided  per  25  junctions.  This  at  the  outgoing  end  is  multipled 
on  every  operator's  keyboard,  and  is  connected  to  her  telephone  by 
pressing  a  small  push-button.  At  the  incoming  end  this  service  wire 
is  connected  direct  to  the  operator's  receiver.  When  a  subscriber 
calls,  the  first-mentioned  operator  connects  with  the  service  wire  and 
informs  the  listening  operator  at  the  other  exchange  the  number 
wanted,  this  operator  allots  the  junction  to  be  used  as  she  knows  by 
the  position  of  the  plugs  what  lines  are  available,  tests  the  line 
wanted,  and.  if  free,  inserts  the  junction  plug,  the  originating  operator 
at  the  same  time  connecting  the  subscriber  to  the  junction  specified. 
The  subscriber  may  be  rung  by  cither  the  originating  or  the  incoming 
operator  but,  preferably,  by  the  latter  and  automatically.  When  the 
clearing  signals  are  received  from  the  subscribers  by  the  originating 
operator  she  withdraws  the  plugs  and  automatically  signals  to  the 
incoming  end,  the  operator  there  then  withdrawing  the  plug  also. 
The  following  is  a  description  of  two  typical  junction  circuits  : — 


798    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

Relay  Ring-through  functions  worked  by  Call  Wire, 

Fig.  2  shows  the  connections  of  a  call  wire  junction  line  between 
two  exchanges  worked  on  the  above  system.  This  diagram  should  be 
considered  in  connection  with  Fig.  14. 

At  the  outgoing  end  A,  a  local  or  subscriber's  cord  circuit  is  shown, 
L  being  the  listening  key,  C  the  bridging  coil,  D  the  250-ohm  clearing 
relay  with  lamp  E  in  parallel,  and  joined  up  so  as  to  retain  when 
pulled  up  by  battery  F. 

A  single  tongued  relay  G  is  connected  to  the  bush  of  the  junction 
jack.  The  insertion  of  a  calling  plug  into  this  jack  operates  relay  G, 
and  thus  cuts  the  earth  off  the  junction  lines  and  bridging  coil  H. 

The  operator  at  the  incoming  end  B  obtains  an  engaged  test 
through  the  tip  of  the  junction  plug  and  one  outer  tongue  of  relay  N, 
on  third  conductor  of  the  plug,  through  tertiary  winding  R  of  her 
induction  coil.  If  there  is  no  click  she  then  plugs  in,  thus  operating 
relay  N,  which  disconnects  the  tip  qf  the  plug  from  the  tertiary  winding 
and  connects  it  direct  to  the  A  line  ;  this  relay  also  joins  clearing  relay 
M  (250  ohms  resistance)  from  the  centre  point  of  retardation  coil  K, 
direct  to  earthed  battery  P. 

The  jack  into  which  the  junction  line  is  plugged  is  that  shown  in 
Fig.  14.  When  the  subscriber  at  the  incoming  end  depresses  his  key, 
the  clearing  relay  D  (Fig.  2)  at  the  outgoing  end  is  brought  up  and 
retained,  thus  giving  the  clear  at  the  outgoing  end. 

When  the  outgoing  operator  withdraws  the  calling  plug  from  the 
junction  jack,  the  relay  G  is  released  and  puts  earth  on  the  centre  point 
of  the  junction  line,  so  that  relay  M  is  actuated  and  the  clearing  lamp 
O  glows. 

When  the  incoming  operator  withdraws  the  plug  from  the  jack, 
the  relay  N  is  released  and  everything  thus  returned  to  the  normal 
condition. 

Central  Battery  Junctions  Worked  by  Call  Wire. 

Fig.  3  shows  the  call  wire  circuit  and  also  the  outgoing  and 
incoming  ends  of  a  junction.  It  will  be  noticed  that  at  the  outgoing 
end  no  relays  are  required  to  join  up  or  cut  off  the  clearing  current,  as 
this  is  already  on  the  lines  on  the  insertion  of  the  plug  q,  (See  Fig.  15.) 
The  bush  or  test  connection  of  the  jack  has  a  30  ohms  resistance  coil 
joined  in  series  to  earth  to  complete  the  circuit  for  the  supervising 
lamp  on  the  calling  plug.  The  call  wire  is  brought  through  a  key  so 
connected  that  adjacent  positions  may  be  joined  together,  and  terminates 
on  the  operator's  instrument.  A  self-restoring  indicator  relay  is  also 
bridged  on  the  line  for  night  use,  in  the  night  bell  contact  of  which  is 
joined  a  lamp,  battery  and  relay  for  calling  when  the  operator  is  not 
listening,  a  special  key  being  fitted  to  restore  the  indicator.  In 
this  system  also  no  listening  or  testing  keys  are  used,  these  being 
replaced  by  a  relay  C  in  the  third  conductor  of  the  cord,  and  an 
induction  coil  with  three  windings  connected  so  that  in  the  normal 
position  the  tip  of  the  plug  is  joined  to  the  tertiary  winding  ready  to 


1903.] 


AN  EFFICIENT  TELEPHONE   SYSTEM. 


799 


receive  the  engaged  click,  and  on  the  insertion  of  the  plug  the  relay 
is  actuated  and  the  tip  is  broken  from  the  induction  coil  and  connected 
through  to  the  line.    This  relay  lis  also  in   circuit  with  the  clearing 
lamp  which  is  12  volts  and  has  resistances  placed  in  series  with  it 
In  this  circuit  a  ringing  control  is  used.    When  the  key  is  depressed 


a  clutch  holds  it  in  that  position  and  connects  up  the  ringing  generator. 
When  the  telephone  is  taken  from  its  rest  an  excess  of  current  actuates 
the  electromagnet  and  releases  the  clutch,  thus  cutting  off  the  genera- 
tor. The  only  other  special  point  in  this  circuit  is  the  method  employed 
for  clearing,  so  that  on  the  called  subscriber  replacing  his  telephone  the 
clearing  signal  may  be  given  right  back  to  the  calling  plug  circuit  at 


800    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

the  originating  exchange,  and  on  this  plug  being  withdrawn  the  clearing 
lamp  in  the  incoming  junction  plug  circuit  glows. 

This  is  accomplished  by  means  of  a  special  relay  G  having  two 
windings,  one  of  very  high  resistance  (12,000  ohms),  so  that  the  supw- 
vising  relay  on  the  calling  plug  at  the  originating  end  will  not  be 
actuated  through  it.  The  other  coil  is  of  low  resistance  to  hold  up  the 
armature  of  the  relay.  This  keeps  the  clearing  lamp  out  by  shunting 
it  with  a  40-ohm  coil.  The  high  resistance  coil  of  relay  g  is  short- 
circuited  by  the  armature  of  the  supervisory  relay  D  in  order  that  the 
line  resistance  may  be  reduced  to  a  minimum,  so  that  the  supervisory 
relay  on  the  calling  plug  at  the  outgoing  end  may  be  actuated  and 


TEST  BOARD 


MULTIIM.E  SWITCHBOARD 


'-•OU  COMItKTHM 


KWlTmi  J*C« 


RELAY  BOARD 


INTERMEDIATE 

DISTRIBUTING 

BOARD 


CALUNG  LAMP  A  LOCAL  JACK 


M 


^     CENTRAL  BATTERY 

'  (M  VOLTI) 


•HiliiilHililh- 


Fig.  4. 


so  keep  the  clearing  lamp  on  that  plug  out  while  the  junction  is 
engaged. 

It  will  thus  be  seen  that  when  the  local  subscriber  on  the  incoming 
junction  has  finished  his  conversation  and  replaces  his  receiver  on  the 
rest,  the  circuit  is  broken  and  the  armature  of  the  supervisory  relay  D 
falls  back,  and  the  high  resistance  coil  of  relay  G  is  placed  in  circuit  in 
the  line.  This  releases  the  supervisory  relay  on  the  calling  plug  at  the 
originating  end  and  causes  the  corresponding  lamp  to  glow.  The  high 
resistance  coil  of  relay  G  is,  however,  during  this  time  still  keeping  its 
armature  attracted,  but  on  the  withdrawal  of  the  calling  plug  at  the 
outgoing  end  this  is  released  as  the  current  is  cut  off,  and  the  lamp 
glows,  giving  the  signal  to  clear. 

The  condenser  placed  in  the  line  side  of  the  repeating  coil  is  used 


1903.] 


AN  EFFICIENT   TELEPHONE   SYSTEM. 


TOl 


to  improve  the  talking,  othenw^ise  the  choking  effect  of  relay  G  would 
make  speech  impracticable. 

We  will  just  glance  for  a  moment  at  the  circuits  of  an  up-to-date 
Exchange — on  the  Common  Battery  System — so  that  you  may  appre- 
ciate the  slight  additional  complications  which  are  made  necessary 
by  the  divided  system  to  be  described.  Fig.  4  shows  the  line  circuit 
of  the  Western  Electric  Company's  system.  Fig.  5  shows  the  line  and 
cut  off  relays  in  detail. 

In  such  a  system  all  lines  are  multipled  on  every  section  of  switch- 
board, each  containing  about  300  subscribers'  lines  served  by  three 
operators.  The  multiple  and  answering  jacks  are  branched  from  opposite 
sides  of  the  intermediate  distributing  board.  A  line  and  cut  off  relay  is 
in  combination  with  each  line.    The  subscriber's  instrument  has  a  con- 


Plan  of  tower  (Cut-off)  Relay 
Fig.  5. 


denser  in  circuit  with  the  bell  normally,  which  prevents  the  central 
battery  discharging.  When  a  call  is  made  by  taking  the  telephone 
from  its  rest,  a  path  is  provided  for  the  current  through  the  microphone 
and  induction  coil,  and  the  line  relay  is  energised.  The  calling  lamp  in 
the  local  circuit  glows,  and  the  operator  answers  by  inserting  a  plug 
into  the  jack  hole  immediately  above  the  lamp.  The  cut  off  relay  is 
then  energised  and  cuts  the  line  relay  out  of  circuit  so  that  the  calling 
lamp  ceases  to  glow.  The  connection  is  completed  by  the  insertion 
of  the  other  plug  of  the  same  cord  into  the  multiple  jack  of  the  line 
wanted.    A  skeleton  cord  circuit  is  shown  in  Fig.  15. 

The  line  and  cord  circuit  of  the  Kellogg  Switchboard  and  Supply 
Company  are  shown  in  Frgs.  6  and  7.  The  peculiarity  of  this  line 
circuit  is  that  there  are  only  two  wires  throughout  the  switchboard 
per  line  instead  of  three  as  is  usual,  and  that  the  lines  are  not  connected 
to  the  multiple  until  the  plug  is  inserted.  The  cut  off  relay  coil  is 
tapped  off  the  line  circuit  instead  of  being  on  the  third  wire.    The 


80^    \1TKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 


o 


Note.— The  blocks  of  Figs.  4,  5,  6,  7,  8,  were  kindly  lent  by  the  Electrician. 


1903.] 


AN   EFFICIENT  TELEPHONE  SYSTEM. 


^08 


cut  off  relay  is  shown  in  detail  on 
Fig.  8. 

Having  now  considered  the 
general  principles  of  the  usual 
methods  of  working,  let  us  consider 
a  concrete  case,  dealing  with  an  area 
served  by  two  large  exchanges. 

Such  a  condition  could  hardly 
exist  in  practice.  There  would 
almost  certainly  be  lines  to  smaller 
and  more  distant  exchanges.  In 
large  systems  it  is  usual  to  reckon 
the  number  of  junctions  necessary 
at  2o  per  cent,  of  the  number  of 
subscribers'  lines  in  an  exchange. 

In  considering  the  following 
hypothetical  case,  I  have  calcu- 
lated on  15  per  cent,  being  neces- 
sary for  working  between  two 
large  exchanges. 

Between  two  exchanges  of 
10,000  lines  each  15  per  cent,  of 
junction  lines  would  be  required, 
7i  for  incoming  work  to  one  ex- 
change and  7i  to  the  other,  or 
1,500  metallic  circuit  lines.  To 
accommodate  the  incoming  junc- 
tions 20  switchboards  (10  in  each 
exchange)  would  be  necessary 
with  25  lines  per  operator  and 
three  operators*  positions  per 
board.  Sixty  operators  and  six 
supervisors  are,  therefore,  required 
to  work  the  incoming  junction 
lines  in  the  two  exchanges,  and 
as  each  subscriber's  operator  has 
a  large  proportion  of  connections 
for  the  other  exchange  she  cannot 
attend  to  so  many  calls  as  she  could 
do  if  all  the  work  were  local.  On 
each  junction  switchboard  the 
complete  multiple  of  10,000  sub- 
scribers' lines  must  be  repeated, 
and  on  every  subscriber's  section 
1,125  spring  jacks  must  be  multi- 
pled  for  outgoing  work  to  the 
other  exchange,  these  being  multi- 
pled  three  times  on  two  sections 
to  place  them  well  within  the 
reach  of  the  operators. 


a&4    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  SOlh, 

The  provision  of  junctions  between  exchanges  is  a  difficult  one,  for 
to  provide  an  ideal  service  the  number  of  circuits  must  be  sufficient  to 
carry  the  maximum  number  of  calls  at  the  busiest  half-hour  of  the 
busiest  day,  and  necessarily  many  of  these  junction  circuits  would  be 
lying  idle  the  greater  part  of  the  time. 

In  the  earlier  days  of  telephony  there  was  not  much  need  for  the 
divided  board,  as  the  great  cities  were  effidently  telephoned  with 
switchboards  having  a  capacity  of  from  6,000  to  15,000  lines.  When 
necessary  a  number  of  these  were  fitted  and  connected  by  junction 
lines.  Even  to-day  the  system  I  advocate  is  worthy  of  consideration 
practically  only  in  the  world's  capitals,  where  it  may  be  expected  that 
the  number  of  telephone  subscribers  may  reacli  something  like  100,000. 

Underground  work  is  essential  with  the  divided  board,  owing  to 


Fig.  8. 


earths,  etc.,  giving  false  calls,  and  it  is  only  of  late  years  that  facilities 
could  be  obtained  for  work  of  such  a  nature,  and  even  to-day  way- 
leave  facilities  arc  not  always  obtainable. 

It  is  only  in  recent  years  also  that  satisfactory  conduits  for  large 
capacities  have  been  introduced,  and  that  hermetically  sealed  lead- 
covered  air-space  paper  cables  containing  a  large  number  of  con- 
ductors were  manufactured.  The  system  I  am  about  to  describe  to  you 
is  just  beyond  the  experimental  stage,  and  I  think  the  time  is  now  ripe 
for  it  to  receive  careful  attention. 

Such  a  system  must,  of  necessity,  be  an  undergrourfd  metallic 
circuit  system.  The  average  length  of  subscribers'  lines  would  be 
greater  with  a  divided  system  than  with  the  junction  system,  as  a 
larger  area  would  be  served  from  a  central,  but  against  this  must  be 
placed  the  great  reduction  in  the  number  of  long  junction  circuits  with 
their  elaborate  switchboard  equipment. 

In  my  opinion,  it  is  only  by  adopting  a  divided  multiple  switchboard 
system  of  working,  in  which  the  exchange  is  divided  into  several 
sections,  the  subscriber  having  the  power  to  call  any  one  of  the  sections 
at  will,  the  large  cities  of  the  world  may  be  more  efficiently  telephoned. 


1903.] 


AN  EFFICIENT  TELEPHONE  SYSTEM. 


805 


806    AITKEN     DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

By  a  divided  multiple  exchange,  I  mean  an  exchange  divided  into 
two  or  more  groups,  each  group  having  a  multiple  of  a  proportion  only 
of  the  total  subscribers'  lines,  each  subscriber  having  the  power  of  calling 
each  of  the  groups  at  will  and  obtaining  connection  with  the  subscribers 
multipled  thereon  without  the  intervention  of  a  second  operator.  The 
advocates  of  the  divided  multiple  board  system  believe  in  centralisation 
and  the  abolition  of  junction  lines  as  far  as  possible.  The  multiple  of 
each  switchboard  or  division  is  made  as  large  as  can  be  convenientiy 
reached  by  the  operator,  and  where  those  who  favour  the  divided 
system  differ  from  the  advocates  of  the  junction  system  is  in  that  they 
ask  the  co-operation  of  the  subscriber  by  giving  him  the  selecting  of 
the  group  of  switchboards  on  which  the  line  wanted  is  connected. 
Two  or  three  push-buttons  or  switches  are  fitted  in  combination  with 
the  ordinary  subscriber's  instrument,  one,  say,  labelled  i  to  10,000,  the 
second  10,001  to  20,000,  and  the  third  20,001  to  30,000,  or  in  other 
suitable  divisions.     In  addition  to  taking  the  telephone  from  the  switch- 


FiG.  10. 


hook  the  subscriber  has  to  press  the  button  of  the  group  in  which  is  the 
number  required ;  he  then  gets  the  connection  direct  instead  of  as  in 
the  junction  system,  the  first  operator  having  to  ask  the  second  to  assist 
her  in  completing  the  connection  in  a  large  proportion  of  the  calls. 

The  central  exchange  on  a  divided  system  consists  really  of  two  or 
more  great  multiple  switchboards  serving  a  large  area,  and  its  total 
capacity  may  be  from  30,000  to  60,000  lines,  according  to  the  size  of 
the  units  and  number  of  divisions.  Instead,  however,  of  having 
junction  lines  between  the  exchanges  the  subscriber's  line  is  branched 
to  each  division  and  has  a  calling  signal  and  answering  jack  on  each, 
so  that  it  can  be  connected  to  each  of  the  multiples  of  the  several 
divisions,  his  own  line  being  multipled  on  one  of  the  divisions  so  that 
other  lines  may  be  connected  to  it.  The  subscriber  can,  therefore, 
greatly  expedite  the  rate  of  operating  for  a  great  proportion  of  his  calls, 
and  at  the  same  time  he  enables  the  operator  to  perform  more  work  as 
a  second  operator  more  rarely  intervenes. 

A  proportion  of  junction  working  will  still  exist  to  the  exchanges 
more  distant  from  the  centre,  but  in  most  instances  it  will  be  possible 


1903.] 


AN  EFFICIENT  TELEPHONE  SYSTEM. 


807 


to  so  design  a  system  that  75  per  cent,  of  the  possible  junction  working 
will  be  eliminated.  I  have,  therefore,  based  my  estimates  on  this 
figure. 

Fig.   I   shows  a  large  populous  area  telephoned  on  the  junction 


i      i  "^ 


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51 


L.^ 


K' 


]^ 


system,  the  total  number  of  subscribers  being  115,000  in  thirty-seven 
exchanges.  The  largest  exchange  has  a  capacity  for  15,000  lines,  or 
13  per  cent,  of  the  total.  In  the  two*largest  exchanges  there  is  22  per 
cent,  and  in  three  26  per  cent.  Even  if  the  three  exchanges  were  each 
of  15,000  lines  they  would  only  contain  39  per  cent,  of  the  whole. 
Vol.  32.  63 


808    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :    [April  30th, 

Fig.  9  shows  the  same  area  telephoned  on  the  divided  multiple 
system  for  the  same  number  of  lines  in  fifteen  exchanges.  The  largest 
exchange  has  45,000  lines  and  the  next  30,000  lines.  In  the  former 
there  is  39  per  cent.,  in  the  two  65  per  cent.,  and  in  three  83  per  cent. 
of  the  total. 

The  lines  on  the  diagrams  indicate  direction  only  and  not  the 
number  of  circuits  necessary. 

I  may  be  accused,  with  a  good  deal  of  justice,  of  comparing  a 


Fig.  12 


theoretically  good  divided  system  (Fig.  9)  with  an  imperfect  junction 
system  (Fig.  i),  but  with  the  latter  system  local  conditions  and  limita- 
tions, such  as  rivers,  public  parks,  low-class  residential  neighbourhood, 
etc.,  form  natural  boundaries  beyond  which  for  the  sake  of  economical 
working  it  is  not  desirable  to  extend,  and  therefore  single  exchanges  of 
the  maximum  size  are  not  always  possible  or  essential,  whereas  this 
does  not  apply  to  the  same  exteift  to  the  former. 

Milo  G.  Kellogg,  of  Chicago,  was,  I  believe,  the  first  to  design  and 
advocate  a  divided  multiple  board   ystem,  and  a  number  of  exchanges 


1908.] 


AN  EFFICIENT  TELEPHONE  SYSTEM. 


809 


are  now  working  in  America  on  this  plan.  Usually  two  divisions 
have  been  adopted,  but  in  one  or  more  cases  a  four  division  board  has 
been  installed.  In  these  pioneer  exchanges  the  system  was  complicated 
by  polarised  relays  and  indicators  on  the  switchboards,  and  at  the 
subscribers'  offices  by  commutated  magneto  generators. 

In  at  least  one  case  the  magneto  generators  were  replaced  by  the 
primary  speaking  battery,  acting  through  an  induction  coil,  giving  a 
"  kick "  when  the  circuit  was  made  and  broken,  sufficient  to  energise 
the  calling  signal  (see  Fig.  lo).  Suitable  switches  connected  the  current 
generating  apparatus  to  line  in  the  proper  direction  to  actuate  the 
signalling  apparatus  in  the  division  required. 

In  one  circuit  a  positive  and  a  negative  polarised  indicator  are  in 
series  across  the  loop  and  two^imilar  indicators  in  series  are  connected 
as  a  tap  to  earth  on  one  wire  of  the  metallic  circuit.    (See  Fig.  ii.) 


Fig.  13. 


In  another  case  a  positive  and  a  negative  polarised  indicator  are  in 
series  and  tapped  to  earth,  two  o£E  each  line.  (See  Fig.  12.)  Four-division 
exchanges  are  thus  obtained. 

With  the  development  of  the  central  or  common  battery  system  of 
telephone  exchange  working  and  the  popularising  of  the  telephone  the 
need  for  a  simpler  way  of  working  great  central  exchanges  became 
more  urgent,  and  when  considering  this  question  I  was  struck  with  the 
idea  of  working  a  divided  system  from  a  central  battery.  I  had 
previously  designed  two  circuits  which  led  naturally  up  to  this,  one 
in  February,  1898,  with  a  retaining  electromagnet  at  the  subscribers' 
instrument,  which  allowed  a  momentary  depression  of  a  key  (thereby 
mechanically  completing  the  circuit  of  the  central  battery  through  the 
calling  relay  to  earth)  to  give  a  permanent  signal  to  the  operator  (Fig.  13) 
and  another  in  June,  1899,  in  which  I  removed  the  electromagnet  from 
the  subscribers'  instrument  and  provided  a  local  retaining  circuit  on  the 
relay  at  the  exchange,  utilising  the  ordinary  line  relay  coil  for  this 
purpose  (Fig.  14). 

The  latter  I  preferred  to  use  for  my  divided  board  system,  as  it 
simplified  the  apparatus  at  the  substation. 

In  this  system  non-polarised  relays  are  used,  energised  from  a 
central  battery  when  any  one  of  the  simple  switches  at  the  substation 


810    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30tll, 


RING    THROUGH    SYSTEM 


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Fig.  14. 


1903] 


AN  EFFICIENT  TELEPHONE   SYSTEM. 


811 


instrument  is  depressed.  The  caller  can  thus  select  any  one  of  two  or 
three  groups  of  multiple  switchboards  required. 

A  greater  number  of  combinations  could,  no  doubt,  be  obtained 
by  step  by  step  movements,  but  at  the  expense  of  simplicity. 

In  a  two-division  exchange  having  two  groups  of  multiple  switch- 
boards, two  simple  single  make-and-break  relays  are  necessary  ^  the 
central  and  two  earthing  or  grounding  switches  at  the  substation. 

In  a  three-division  exchange  two  double  (or  one  triple  and  one 
double)  make-and-break  relays  are  used  in  connection  with  the  two 
wires  of  the  metallic  circuit,  and  in  connection  with  them  are  three 
calling  lamps,  one  on  each  of  three  groups  of  multiple  switchboards. 


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Fig.  15. 


L^D.- 


Any  of  the  well-known  forms  of  instruments  may  be  used  in  conjunc- 
tion with  these  systems,  it  being  only  necessary  to  fit  in  combination 
therewith  a  simple  two-  or  three-way  switch  as  required,  one  position 
earthing  the  A  line,  another  earthing  the  B  line,  and  the  third  earthing 
the  A  and  B  lines  simultaneously  (the  latter  in  the  three-division  only). 
The  switch-lever  or  plunger  is  put  momentarily  in  one  of  these  posi- 
tions to  give  a  permanent  signal  to  the  attendant  at  the  corresponding 
switchboard. 

With  a  two-division  system,  shown  in  skeleton  on  Fig.  15  and  the 
line-circuit  in  more  detail  on  Fig.  16,  two  switchboards,  A%  B'(Fig.  15), 


819    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

of  suitable  size  are  provided,  and  one-half  the  total  capacity  is  multipled 
on  one  line  of  boards  and  half  on  the  other.  Each  subscriber's  instru- 
ment has  two  push-buttons,  A',  B',  one  for  earthing  the  A  and  the  other 
for  earthing  the  B  line. 

Each  line,  after  passing  through  the  usual  test-board  or  main 
distributing  frame.  T.B.  (Fig.  i6),  is  connected  to  a  special  double 
intermediate  distributing  frame,  I.D.B.  To  a  central  set  of  soldering 
tabs  the  two  test-board  wires  are  connected,  and  from  the  same  set  a 
triple  wire  per  circuit  is  carried  to  the  multiple  jacks,  M.J.,  of  one  line 
of  boards.  From  a  parallel  strip  of  tabs  on  one  side  of  the  central  line 
tabs  a  quadruple  wire  per  circuit  is  carried  to  the  answering  jack,  A. J.*, 
and  calling  lamp,  C.L.',  on  the  same  line  of  boards  and  from  a  parallel 
line  of  tabs  on  the  other  side  of  the  central  line  tabs  another  quadruple 
wire  per  circuit  is  carried  to  an  answering  jack,  A.].',  and  calling  lamp, 
C.L.»,  on  the  second  hne  of  board.  A  quad-cross-connecting  wire 
connects  the  central  line  tabs  and  the  tabs  on  both  sides.  All  wires 
from  the  intermediate  frames  are  made  up  in  cables,  but  the  wires 
between  tabs  are  made  in  loose  quads  to  allow  of  ready  alteration  with 
the  object  of  changing  the  local  position  of  any  subscriber  so  as  to 
equalise  the  work  per  operator,  as  in  this  arrangement  it  is  necessary 
to  allow  distribution  on  each  line  of  boards.  Each  quad  is  made  up  of 
the  two  hne  wires,  the  test  wire  and  a  lamp  wire.  The  test  wire  also  has 
a  connection  through  the  cut-off  relay  coil  to  earth.  Each  line  wire  has 
a  connection  through  a  tongue  and  contact  of  the  cut-off  relay,  C.O.R., 
and  its  line  relay  coil,  L.R.'  or  L.R.«,  to  battery  and  earth.  E^h 
tongue  of  the  cut-off  relay,  C.O.R.,  has  also  a  connection  to  the  tongue 
of  the  line  relay  associated  with  it,  the  under-contact  of  each  hne  relay 
being  connected  to  earth. 

The  answering  jacks  and  calling  lamps  are  arranged  in  the  usual 
way,  with  pilot  relay,  P.R,  and  lamp,  P.L.,  night-bell,  N.B.,  etc.,  as 
shown  at  Fig.  i6.  The  calling  lamp  has  also  a  connection  to  the  line 
side  of  the  relay  coil,  so  tl^at  it  is  in  parallel  with  that  coil.  The  action 
is  as  follows  : — 

When  a  subscriber  depresses  key  A'  (Fig.  15)  there  'is  a  circuit 
from  the  earthed  central  battery  through  line  coil  of  relay,  k  (with 
lamp,  j,  in  parallel)  associated  with  that  Hne,  through  one  contact 
and  tongue  of  cut-off  relay,  h,  through  the  A  wire  to  earth  at  key  A'. 
The  line  relay,  k,  is  therefore  energised  and  the  lamp,  j,  glows.  There 
is  then  a  local  circuit  from  earthed  central  battery  through  line  coil,  k, 
and  lamp,  j,  in  parallel,  through  contact  and  tongue  of  cut-off  relay,  h, 
through  tongue  and  contact  of  line  relay,  k,  to  earth,  and  the  lamp, 
therefore,  continues  to  glow  after  the  key  A'  is  released  until  the 
operator  answers.  This  is  done  by  inserting  a  plug,  q,  of  a  connection 
set  into  the  answering  jack,  C*.  Another  local  circuit  is  then  estab- 
lished from  earthed  central  battery,  i,  through  the  shunted  lamp,  p,  on 
the  third  conductor  of  the  cord  to  sleeve  of  plug,  q,  bush  of  jack,*C, 
over  test  wire,  through  cut-off  relay  coil,  h,  to  earth.  The  cut-off  relay, 
h,  is,  therefore,  energised  and  the  hne  relay  circuit  broken  by  the 
tongue  leaving  the  outer  contact,  so  that  the  caUing  lamp  ceases  to 
glow.    The  subscriber  may  then  be  connected  with  any  other  on  that 


X903.] 


AN  EFFICIENT  TELEPHONE  SYSTEM. 


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814     AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

multiple.  Should  the  B»  key  be  depressed,  the  other  line  relay  and 
lamp  will  be  energised,  the  retaining  circuit  be  broken  by  the  cut-off 
relay  being  energised  by  a  connecting  set  used  by  an  operator  at  the 
second  line  of  boards,  and  a  connection  completed  thereon. 

Each  operator  may  have  300  answering  jacks  and  calling  lamps 
under  her  control,  but  will  only  attend  to  half  the  total  number  of  calls 
from  each  subscriber. 

As  there  are  fewer  junction  lines  between  exchanges  on  the  divided 
system,  the  outgoing  junction  work  will  be  less  and  each  local  operator 
will  therefore  be  able  to  attend  to  a  greater  number  of  lines. 

Presumably  on  the  junction  system  about  50  per  cent,  of  the  calls 
would  be  for  the  second  exchange,  and  as  a  junction  call  takes  twice  as 
long  to  complete  as  a  local  one,  if  most  of  the  work  is  made  local,  as  oa 
the  divided  system,  the  operator  will  be  able  to  attend  to  approximately 
50  per  cent,  more  lines,  so  that  instead  of  66'/3  subscribers*  sections 
being  necessary  on  the  junction  system  at  100  lines  per  operator, 
only  44V3  sections  would  be  necessary  on  the  divided  system. 

There  will  also  be  a  very  considerable  saving  in  floor  space,  and 
consequently  rent  or  value  of  premises,  as  the  length  of  the  unnecessary 
junction  and  subscribers'  sections  would  be  about  270  lineal  feet,  made 
up  of  20  junction  sections  and  22  subscribers'  sections,  each  about 
6  ft.  6  in.  long. 

If  three  10,000  line  exchanges  were  opened  on  the  junction  S3rstemthen 
possibly  treble  the  number  of  junction  lines,  multiple  junction  sections, 
and  operators  would  be  necessary,  as  1,500  lines  are  required  between 
A  and  B,  1,500  between  B  and  C,  and  1,500  between  A  and  C,  and  the 
subscribers'  (or  local)  operators  can  each  attend  to  a  still  smaller 
number  of  calls,  because  a  still  greater  proportion  of  their  work  is  over 
junction  lines,  and  each  local  operator  would  then  be  able  to  attend  to 
a  smaller  number  of  lines,  say  90  instead  of  100.  The  number  of 
switchboards  and  number  of  operators  would  therefore  be  increased, 
while  there  would  be  no  increase  on  the  three-division  system. 

With  a  three-division  system,  shown  in  skeleton  on  Fig.  17  and  in 
detail  on  Fig.  18,  at  the  central  exchange  three  independent  multiple 
switchboards  are  fitted,  one-third  of  the  total  number  of  lines  being 
multipled  on  each.  Each  subscriber's  line  is  multipled  on  one  of  the  three, 
but  has  an  answering  jack  and  calling  lamp  (or  other  indicator)  on  each. 
An  operator  may  therefore  have  450  calling  lamps  and  answering  jacks 
to  attend  to— 150  in  connection  with  the  lines  multipled  on  that  group 
of  switchboards  and  150  each  in  connection  with  the  other  two  groups, 
so  that  the  subscribers  can  call  and  be  connected  to  the  other  lines 
that  are  multipled  thereon.  Three  relays,  as  before,  are  required  for 
each  circuit,  one — the  cut-off  relay,  C.O.R.  (Fig.  18) — having  two 
springs  which  are  made  to  break  from  two  contacts,  as  before,  by  the 
action  of  the  armature  when  the  relay  is  energised.  The  coil  has  one 
side  connected  to  the  earthed  side  of  the  central  battery  and  the  other 
side  connected  to  the  test  circuit  of  the  spring  jacks,  as  is  usual.  The 
two  line  relays  differ  from  those  of  the  two-division  board  and  more 
nearly  resemble  the  cut-off  relay.  One  has  two  springs  which  break 
from  one  and  make  on  two  contacts  when  energised,  the  other  has 


1908.J 


AN   EFFICIENT  TELEPHONE  SYSTEM. 


815 


three  springs  which  break  from  one  and  make  on  two  contacts  when 
energised.  This  modification  from  Fig.  17  was  necessary  to  get  a 
common  circuit  from  pilot  relay,  P.R.3. 

The  coil  of  each  line  relay,  L.R.,  has  one  side  connected  to  the 
earthed  central  battery,  the  other  side  being  connected  to  the  outer 
contacts  of  the  cut-off  relay,  C.O.R.  The  relay  tongues  or  moving 
springs  of  the  cut-off  relay  are  connected  one  to  each  line,  each  also 
having  parallel  extensions  to  one  of  the  tongues  of  its  respective  line 
relay ;  these  tongues,  when  the  relays  are  energised,  make  contact  with 
inner  points  connected  to  the  earthed  side  of  the  central  battery.  A 
small  incandescent  lamp,  C.L.',  connected  with  the  No.  i,  or  A,  group 
of  boards  is  in  parallel  with  the  coil  of  one-line  relay,  L.R.»,  and  a 
second  lamp,  C.L.',  in  connection  with  the  No.  2,  or  B,  group  of  boards, 
in  parallel  with  the  coil  of  the  other  line  relay,  L.R.*.    The  line  relays 


Fig.  17. 


have  another  tongue,  which  rests  normally  against  an  outer  contact, 
but  when  actuated  by  the  armature  when  the  relay  is  energised  breaks 
from  this  point  and  makes  contact  with  another.  Normally  the  circuit 
of  the  A  and  B  lamps  are  completed  through  these  contacts.  When, 
however,  the  relay  L.R.'  immediately  associated  with  the  A  group  of 
boards  is  energised  the  circuit  of  the  B  lamp  C.L.'  is  cut ;  similarly, 
when  the  B  relay  L.R.*  is  energised  the  A  lamp  C.L.'  circuit  is  cut  and 
if,  therefore,  both  relays  be  energised  at  the  same  time  the  circuits  of 
both  lamps  will  be  cut.  The  circuit  of  the  lamp  C.L.3  in  connection 
with  the  No.  3,  or  C,  group  of  boards  is  then  established,  the  circuit 
then  being  from  the  earthed  central  battery  through  pilot  relay,  P.R.3, 
through  the  tongue  and  inner  contact  of  the  line  relay,  L.R.',  through 
I.D.B.,  through  the  C  lamp  to  the  inner  contact  and  tongue  of  the  line 


816    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

relay,  L.R.»,  through  the  right-hand  outer  contact  and  tongue  of  the 
cut-off  relay,  C.O.R.,  and  the  other  tongue  and  under-contact  of  the 
line  relay  L.R'  to  earthed  side  of  battery. 

Samples  of  suitable  relays  are  on  the  table.  With  modern  improve- 
ments the  dread  of  double  and  triple  contact  relays  has  disappeared. 

At  the  substation  three  push-buttons  are  fitted  (Fig.  17),  and, 
according  to  the  number  required,  the  subscriber  presses  the  A',  B% 
or  O  key.  When  the  A*  or  B»  key  is  depressed  the  A  or  B  calling 
lamp  glows,  as  described  for  the  two-division  arrangement,  and  when 
the  C  key  is  depressed  both  lines  are  earthed  and  both  line  relays  are 
energised,  the  circuit  of  the  A  and  B  line  lamps  is  cut  and  the  lamp 
associated  with  the  third,  or  C,  group  of  boards  glows.  When  an 
answering  plug  is  inserted  the  cut-off  relay  is  energised  and  the  local 
retaining  circuits  are  broken  and  the  C  lamp  ceases  to  glow. 

The  foregoing  arrangement  can  be  used  practically  with  any  cord 
circuit.  The  following  are  a  few  examples.  In  the  ring-through  cord 
circuit  (Fig.  2)  the  cord  is  bridged  by  a  suitable  differential  retardation 
coil  C,  having  its  centre  point  connected  through  the  coils  of  a  relay 
D,  to  the  earthed  central  battery,  a  lamp  E  being  in  parallel  with  this 
coil.  The  side  of  the  relay  coil  farthest  from  the  battery  should  be 
connected  to  the  contact  of  the  relay,  the  tongue  connected  through  a 
spring  and  contact  of  the  listening  key  L  to  earth,  so  arranged  that 
the  relay  circuit  may  be  broken  in  the  listening  position.  When  a 
connection  is  made  and  any  one  of  the  plungers  at  the  substation  is 
depressed  momentarily  the  armature  of  the  relay  is  attracted  and  a 
local  circuit  established  which  retains  the  armature,  and  therefore  the 
clearing  lamp  glows  until  the  operator  brings  the  key  to  the  listening 
position  or  withdraws  the  plug. 

This  arrangement  may  be  used  in  conjunction  with  the  ring-through, 
system,  in  which  one  subscriber  rings  the  bell  of  the  subscriber  wanted 
or  the  operator  may  do  the  ringing.  In  the  former  case  a  generator  is 
supplied  with  each  instrument,  in  the  latter  case  this  is  not  necessary. 

In  the  ring-through  system  with  relay  and  lamp  which  was  designed 
to  replace  the  now  practically  obsolete  call-wire  system  I  preferably 
use  a  cord  circuit  without  listening  key  as  shown  on  Fig.  14. 

The  operator's  telephone  is  normally  in  circuit  through  the  back 
contacts  of  a  triple  relay  in  the  third  conductor  of  the  cailing  cord. 
The  operator  is  therefore  ready  to  answer  immediately  she  inserts  the 
answering  plug,  but  when  the  connection  is  completed  by  the  insertion 
of  the  second  plug  her  telephone  is  automatically  cut  out,  as  a  local 
circuit  is  completed  from  earthed  battery,  through  coil  of  triple  relay, 
through  sleeve  of  plug,  bush  of  •  jack,  over-test  wire,  through  coil  of 
cut-off  relay  to  earth. 

This  combination,  it  is  believed,  will  form  the  simplest  manually 
operated  switchboard  known.    The  operating  is  as  follows  : — 

(a)  When  the  lamp  glows  operator  inserts  answering  plug. 

(b)  Tests  line  wanted,  and  if  free  inserts  plug  into  jack  of  line 

wanted. 

(c)  When  clearing  lamp  glows  she  withdraws  plugs. 


1908.] 


AN  EFFICIENT  TELEPHONE   SYSTEM. 


817 


.TB 


-^^0   1    ii_L...L.i. 

thttt 


trr.-j' 


.^1 


Fig.  i8. 


818      AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  30th, 

Such  a  system,  up  to  the  present,  has  only  been  proposed  with 
central  battery  signalling,  a  primary  battery  at  the  subscriber's  being 
used  for  speaking. 

The  divided  board  system  will  work  also  most  efficiently  with  the 
Western  Electric  Company's  common  battery  cord  circuit  when  auto- 
matic clearing  on  two  lamps  and  speaking  from  central  battery  are 
obtained.    (Fig.  15.) 

With  the  circuits  of  the  Kellogg  Switchboard  and  Supply  Co.,  Fig.  7 
it  will  also  work  excellently ;  in  fact,  this  company  have  specially  laid 
themselves  out  for  building  large  exchanges  on  this  system.  Their  circuits 
have  only  two  wires  in  the  multiple  and  two-way  plugs,  and  they  have, 
therefore,  been  able  to  reduce  the  size  of  their  standard  spring  jacks  to 
three-tenths  of  an  inch  face  measurement  instead  of  the  f  in.  as  is 
usual,  and  I  believe  they  are  now  manufacturing  switchboards  of 
20,000  capacity  per  division. 

I  would  propose  forming  one  huge  central  exchange  of  from 
30,000  to  60,000  lines  in  the  heart  of  each  great  city,  this  exchange 
serving  an  area  of  about  14  square  miles  ;  this,  of  course,  would  vary 
with  the  density  of  the  population,  and  the  prospective  number  of 
renters.  With  an  underground  system,  and  cables  containing  from 
250  to  300  pairs  each,  such  an  arrangement  is  perfectly  feasible.  Four 
main  conduits  should  radiate  from  the  central  building,  each  containing 
from  50  to  80  ducts,  these  branching  out,  as  required,  up  to  a  distance 
of  from  2  to  2|^  miles  from  the  exchange.  Outside  this  area,  say  at  2i 
miles' distance  from  the  central,  subsidiary  exchanges  should  be  formed. 
•When  these  exchanges  are  of  considerable  size  they  would  have  direct 
junction  lines  to  the  central,  and  incoming  junction  sections  on  each  of 
the  three  multiples  of  the  central  exchange  ;  where,  however,  the 
junction  lines  were  few  the  operator  would  call  the  multiple  required 
at  the  central  by  pressing  the  corresponding  key  in  the  same  way  as  a 
subscriber. 

The  outgoing  junctions  for  these  subsidiary  exchanges  would  only 
be  multipled  over  one  group  of  boards  at  the  central,  say  the  C  group, 
so  that  subscribers  would  call,  say,  numbers  i  to  16,000  by  depressing 
the  A  key,  16,001  to  32,000  by  depressing  the  B  key,  and  32,001  to 
45,000  and  all  subsidiary  exchanges  by  depressing  the  C  key.  These 
numbers  of  lines  can  perfectly  well  be  placed  within  the  reach  of  the 
operators  by  using  for  the  A  and  B  multiples  6  feet  3  inch  frames 
having  9  panels  of  strips  of  20  spring  jacks  measuring  8^^  inches  by 
i  inch.  Eighteen  blocks  of  100  jacks  give  a  height  of  about  2  feet 
9J  inches.  The  answering  jacks  and  calling  lamps  and  number  pegs, 
in  strips  of  20,  with  space  sufficient  for  533  lines  per  operator  (this 
being  about  equal  to  177  lines  on  a  simple  multiple,  as  each  operator 
only  attends  to  one-third  of  the  total  number  of  subscribers'  calls  on  a 
three-division  system)  would  occupy  a  height  of  about  iij  inches,  so 
that  the  height  of  the  upper  row  of  spring  jacks  above  the  keyboard 
would  be  about  3  feet  9  inches. 

The  C  line  of  boards  could  cither  be  made  to  accommodate  a 
slightly  smaller  number  of  subscribers'  lines,  so  as  to  leave  room  for 
the  outgoing  junctions,  or  the  section  could  be  still  further  increased  in 
^,ngth. 


1D03.]  AN  EFFICIENT  TELEPHONE  SYSTEM.  819 

For  a  45>ooo  line  three-division  exchange,  reckoning  that  each 
operator  can  attend  to  an  average  of  150  lines  per  multiple  board,  or  a 
total  of  450  lines,  the  A  and  B  groups  would  each  consist  of  107 
multiple  sections  ;  while  reckoning  that  each  operator  at  the  C  group 
could  attend  to  100  lines  only  owing  to  the  amount  of  junction  work, 
130  sections  would  be  necessary. 

E^ch  group  of  switchboards  (and  possibly  also  separate  intermediate 
and  main  distributing  frames)  should  preferably  be  in  a  separate  fire- 
proof room  in  practically  separate  buildings,  so  that  in  case  of  fire  the 
fireproof  doors  between  could  be  closed  and  so  confine  the  breakdown 
to  one  group. 

The  premises  should,  therefore,  consist  of  one  central  building  with 
flanking  wings.  In  the  basement  of  the  central  building  one  main 
distributing  frame  should  be  fitted,  arranged  radially  in  four  sections 
of  12,000  or  15,000  in  the  shape  of  a  Greek  cross,  the  four  conduits 
opening  out  at  the  ends.  On  the  ground  floor  should  be  similarly 
arranged  the  intermediate  distributing  board  and  relay  racks,  the 
former  having  two  or  three  distributing  fields,  as  it  may  be  necessary 
for  equalising  purposes  to  cross-connect  the  lines  on  one  group  of 
boards  and  not  on  the  other.  In  the  central  building  might  be  the  C 
switch  room,  the  A  and  B  switch  rooms  being  in  the  right  and  left 
wings  respectively.  Preferably  the  groups  or  divisions  of  the  exchange 
should  grow  uniformly,  as  will  be  made  clear  by  the  following  example. 
If  it  is  desired  to  convert  a  9,000-line  ordinary  exchange  into  a  two- 
division  exchange,  and  it  is  necessary  to  begin  the  second  group  with  a 
capacity  of  2,000  lines,  then  whilst  it  is  only  necessary  to  provide  2,000 
extensions  of  answering  jacks  and  lamps  on  the  9,000-line  frame,  for 
which  there  is  plenty  of  room,  the  9,000  lines  require  lamps  and  jack 
extensions  on  the  sections  built  for  2,000,  and  each  operator  would  have 
an  abnormal  number  of  lamps  and  jacks  from  the  first  line  in  front  of 
her,  and  these  would  require  to  be  redistributed  when  further  extensions 
were  made. 

I  think  it  must  be  granted,  from  what  I  have  said  that,  from  an 
operating  point  of  view  a  great  boon  would  be  obtained. by  the  introduc- 
tion of  the  Divided  Multiple  Board  System.  Also  that  the  made-up  or 
speaking  circuits  would  be  much  simpler. 

^  far  as  I  can  see  the  principal  objection  that  can  be  urged  against 
It  is  that  the  system  depends  for  its  efficient  working  upon  the  co- 
operation of  the  subscribers.  We  have  been  told  that  "men  are 
mostly  fools."  Must  this  be  taken  literally  ?  I  think  at  any  rate,  not 
sufficiently  fools  to  spoil  a  divided  system  by  wilfully  or  carelessly 
calling  on  the  wrong  group  or  division  of  the  exchange. 


820    AITKEN.:  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [Apri! 

COMPARATIVE  ESTIMATE  OF  EQUIPMENT  NECESSARY 
FOR  TWO  IS.OOO-LINE  EXCHANGES  CONNECTED  BY 
JUNCTIONS  AND  ONE  3o,ooo.LINE  TWO-DIVISION 
EXCHANGE. 


Apparatus  for  two 

Apparatus  for  a 

iSooo-Une 

Description  of  the  Apparatus. 

30,000-linc 

Exchanges. 

Exchange. 

30 

Incoming  junction  sections  (at  7^  %) 

None 

100 

Subscribers'  sections          

66} 

1,950,000 

Multiple  spring  jacks         

63  wire  cable  (30  yds.  I.D.B.) 

1,000,000 

337,500  y<is. 

195,000 
None 

168,750 

Outgoing  junction  jack3    

40,500  yds. 

33  wire  cable           

,» 

30,000 

Answering  jacks      

60,000 

30,000 

Calling  lamps          

60,000 

.    30,000 

Double  cut-ofF  relays         

30,000 

30,000 

Line  relays 

60,000 

175,500  yds. 

L     .       .                               ( 

198,000 

(1,500  lengths 
at  117  yds.) 

V84  wire  cable           < 

(3,000  lengths 

J                                                             ( 

X  66  yds.) 

2,250 

M.C.  junctions  x  lengfh  X 

None 

2,250 

Repeater  coils  for  junctions 

„ 

2,250 

Condensers  for  junctions 

2,250 

Relays  (12,000  ohm  +  20  ohm)     ... 

2,250 

Relays  (local  clearing)       

Relays  (on  third  conductors) 

2,250 

2,250 

Clearing  lamps        

2,250 

40-ohm  resistance  coils      

2,250 

30-ohm  resistance  coils      

C  Call  wires  between  Exchanges  with  ) 
(     equipment ) 

90 

2 

Lines  of  tabs  on  I.D.B 

3 

I 

Cross  connecting  wire  per  line    ... 

2 

Twin  switches  on  instruments     ... 

30,000 

390 

Operators      

200 

39 

Supervisors 

20 

845  ^t. 

Length  of  switchboard      

(Practically      the      two-division 
equipment   can   be   fitted   in  a 
building  necessary    for   one   of 
the   15,000-line  Exchanges,  and 
therefore  there  would  be  a  great 
saving  in  cost  or  rent  of  buildings.) 

433  ft.  4  in. 

1 

Increased  length  of  lines 

X  X  15,000      1 

(If  the  2,340  junctions  and  call- 

wires  were  each  two  miles  long. 

this  would  be  equal  to  an  average 

increase  in  the  length  of  each 

of  the  additional  15,000  lines  of 

550  yards.) 

Mileage  of  wire  saved  in  the  two-  ) 
division  Exchange ) 

5,707 

(This  used  outside  would  increase 

the  average  as  above  to  about 
880  yards^ 

75 

Value  of  service       

100 

2 

Power  Plant  with  maintenance    ... 
(Great  economy  will  be  effected 
by  using  one  large  Power  Plant 
instead  of  two  smaller  ones.) 

I 

2 

Power  Board  Staff 

I 

2 

Engineers-in-charge           

^ 

1903.]  AN   EFFICIENT  TELEPHONE  SYSTEM.  821 


TABLE  OF  CONTENTS. 

PAGE 

Cable  work  essential  for  Divided  System      804 

Cord  circuit  for  Ring-through  System  816 

Cord  Circuit  C.  B.  System,  W.  E.  Co's 818 

KeUogg     818 

Description  of  Single  Multiple  Exchange      801 

Description  of  two  Division  Exchange  811 

Description  of  three  Division  Exchange        814 

Distributing  Board  (Intermediate)      812 

Divided  Multiple  Boards,  Area  served  by     806,  818 

„  „  „        Allocation  of  lines  to  operators 814 

„  „  „        Cable  work  essential       804 

„  „  „        Central  Battery 809 

„  „  „        Centralisation       806 

„  „  „        Definition  of         806 

„  „  „        Essential  for  World's  Capitals 805 

„  „  „        Inventor  of  808 

„  „  „        Incoming  Junctions        818 

„  „  „        Indicators  with 809 

„  „  „        Line  circuit  811 

„  „  ,,        Outgoing  Junctions         818 

„  „  „        Possible  size  of     •  806 

„  „  „        Subscriber's  Lines,  Length  of 806 

„  „  „        Subscriber's  office  equipment   ...        811,816 

„  „  „        Subscriber's  operating 816 

„  „  „        Suitable  buildings  for     819 

Divisions  should  grow  uniformly         819 

Junction  Calls,  Slow  down  service      795,  814 

Junction  Calls,  Repetition  of  numbers  795 

Junction  Lines,  Apparatus         797 

Junction  Lines,  In  relation  to  Switchboards  and  Operators         ...  803 

„       Increased  cost  of  equipment  797 

„"      (Incoming)  on  Divided  System      818 

„       Operating  on  Divided  System        806 

„       Outgoing  and  Incoming       796 

„       (Outgoing)  on  Divided  System       818 

,.       Proportion  of,  to  Subscriber's  Lines  796 

„       Provision  of     804 

„       Reduction  of  by  Divided  System 807 

KcUogg,  Milo  G 808 

Kellogg  Switchboard  and  Supply  Co. 's  System        80 1 

Manually  Operated  System,  Simplest  816 

Relays  for  Straight  C.  B.  Board  801 

„        „  Two  Division  Board  811 

„        „  Three  Division  Board         811, 814 

Ring-through  System,  E.  M.,  on  subscriber's  instrument 809 


822     AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :    [April  SOlh, 


PAGE 

8ii 

796 

Telephoning  an  Area,  Usual  method  795>  S08 


Ring-through  System,  Earthing  Key  ... 
Junction  circuit 


Divided  Board  Method 

Western  Electric  Go's  C.  B.  junction  circuit 

„  „  M     System 

References. 

Patent  No.  4699,  March  25,  1890.    M.  G.  Kellogg. 
Patent  No.  5,928,  March  30,  1900.    W.  Aitken. 
Patent  No.  10,124,  June  i,  1900.    J.  E.  Kingsbury. 
Patent  No.  18,031,  October  18,  1900.    Milo  G.  Kellogg. 


808 

798 
801 


Mr. 

Laws  Webb. 


Mr.  Herbert  Laws  Webb  :  I  have  read  Mr.  Aitken's  paper  with  a 
great  deal  of  interest.  The  telephoning  of  very  large  cities  is  a  subject 
which,  of  course,  telephone  engineers  look  at  as  a  daily  increasing 
problem.  I  am  quite  sure  that  all  telephone  men  must  admire  the 
ingenious  manner  in  which  Mr.  Aitken  has  worked  out  the  circuits  erf 
the  divided  multiple  system  to  adapt  them  to  common  battery  working. 
However,  on  the  broad  lines  of  the  problem  my  opinion  is  that  it  is 
working  in  the  wrong  direction  to  advocate  divided  multiple  exchanges. 
In  the  first  place,  such  a  system  largely  increases  the  line  plant.  It 
must  necessarily  greatly  increase  your  average  length  of  subscribers' 
line  if  you  divide  your  city  up  into  very  large  districts,  and  I  think  it 
will  be  found  in  all  large  telephone  systems  that  the  line  plant  repre- 
sents  by  far  the  greater  proportion  of  the  cost  of  the  whole  plant.  I 
think  even  where  line  costs  are  the  cheapest  the  percentage  of  cost  of 
the  liAe  plant  is  about  60  per  cent,  of  the  cost  of  the  whole  system,  and 
to  save  in  the  exchange  plant,  which  is  the  smaller  item  of  cost,  and 
increase  in  the  line  plant,  seems  to  me  to  be  working  in  the  wrong 
direction  as  far  as  cost  is  concerned.  I  think  in  very  large  cities,  where 
it  is  well  known  that  the  expense  of  building  underground  lines  is  much 
greater  than  in  smaller  places,  that  would  bar  out  the  divided  multiple 
board  altogether  on  the  question  of  capital  cost.  The  other  point  that 
seems  to  me  to  be  very  largely  inadvisable  with  this  system  is  that  it 
puts  back  the  operating  of  the  service  into  the  hands  of  the  subscriber. 
W^ith  the  common  battery  we  have  practically  taken  the  operation  of 
the  service  entirely  out  of  the  hands  of  the  subscriber.  The  subscriber 
has  the  simplest  action  to  perform ;  lifting  the  telephone  off  the  support, 
which  he  must  do  in  order  to  use  it,  automatically  gives  the  calling 
signal,  and  in  replacing  the  telephone,  which  I  suppose  999  out  of  1,000 
do  properly,  he  automatically  gives  the  signal  to  disconnect  That 
gives  us  undoubtedly  the  cleanest,  the  quickest,  and  the  simplest  service 
that  it  is  possible  to  give.  In  all  systems  where  part  of  the  operating 
is  done  by  the  subscriber  there  are  numerous  troubles  due  to  the  sub- 
scrit)er's  lack  of  proper  care  in  operating.  If  you  put  these  two  or 
three  buttons  on  every  instrument  for  the  subscriber  to  press  according 


19(».]     AN  EFFICIENT  TELEPHONE  SYSTEM  :  DISCUSSION.       823 

to  whether  he  wants  one  number  or  another,  in  very  many  cases  he  will  Mr. 
press  the  wrong  button  and  get  the  wrong  operator.  Then  you  may 
expect  something  like  this  to  happen  :  the  subscriber  gives  the  number 
that  he  wants,  and  the  operator  says,  "  You  have  pressed  the  wrong 
button."  He  says,  **  What  ? "  Then  the  operator  gets  a  little  more 
impatient,  and  says  rather  shortly,  "  You-have-pressed-the- wrong- 
butt  on  ! "  And  the  subscriber  sa)rs,  "  Hang  your  buttons !  Why 
can't  you  give  me  my  number?"  In  a  great  many  cases  that 
is  bound  to  be  what  would  happen,  more  or  less.  The  language 
in  some  cases  would  be  worse,  and  in  other  cases  it  would  be 
better.  Consider,  for  instance,  one  of  Mr.  Aitken's  proposed  world's 
capitals  systems  of  115,000  subscribers.  You  would  have  an  average 
daily  traffic  there,  at  flat  rates,  of  well  over  one  million  calls.  All  of 
those  million  calls  would  not  come  from  expert  subscribers.  It  is  not 
always  the  man  who  signs  the  contract  who  uses  the  telephone ;  it  is 
used  by  all  sorts  of  people,  from  the  office  boy  down — or  up,  according 
to  which  •way  you  look  at  it— and  it  is  used  very  largely  by  strangers. 
Every  world's  capital  always  has  a  large  floating  population,  and  if  you 
have  115,000  telephone  stations  you  would  have  a  large  number  of 
public  stations,  so  that  a  large  proportion  of  your  daily  traffic  would 
be  from  people  who  are  not  expert  in  using  that  particular  system. 
Therefore  a  pretty  fair  percentage  of  your  million  calls  a  day  would  be 
calls  that  would  be  sent  in  wrongly.  That  would  give  trouble ;  that 
would  need  extra  attention,  unprofitable  work  on  the  part  of  the 
operators  and  the  supervisors  and  the  rest  of  the  exchange  staff.  I 
do  not  think  that  you  can  plan  out  any  telephone  system  nowadays — 
we  have  learnt  something  of  late  years  of  the  telephone-using  public — 
without  keeping  a  very  careful  eye  on  the  public  and  on  what  it  does 
with  the  telephone  at  the  public  end  of  the  system. 

There  are  one  or  two  points  that  occur  to  me  in  Mr.  Aitken's 
estimates  of  operating  values.  I  noted  somewhere  that  he  reckons  a 
junction  call  as  being  the  equivalent  in  time  of  two  local  calls.  That 
seems  to  me  quite  excessive — that  it  should  take  twice  as  long  to  operate 
a  junction  call  as  a  local  call  completed  at  the  same  switchboard.  The 
experience  in  New  York,  which  for  the  past  eighteen  months  or  so  has 
had  uniform  common  battery  working,  is  that  the  difference  in  time 
between  completing  a  local  call  and  a  junction  call  is  nothing  like  so 
much  as  that.  The  very  careful  tests  made  of  a  large  number  of 
connections,  and  tabulated  with  great  care,  show  that  the  actual  time 
is  23  seconds  odd  for  a  local  call  and  30  seconds  for  a  junction  call. 
There  is  almost  exactly  7  seconds  difference  between  them.  That  is,  a 
junction  call  does  not  take  longer  than  i  more  than  the  local  call.  That, 
of  course,  gets  rid  of  a  good  deal  of  the  argument  in  favour  of  the 
divided  multiple  board.  If  your  junction  call  does  not  take  longer  than 
30  seconds  to  operate,  there  is  not  a  very  strong  argument  against 
junction  working.  As  a  matter  of  fact,  having  the  relay  system  in  use 
uniformly,  so  that  all  the  exchanges  are  worked  on  the  same  system, 
and  all  the  operators  are  trained  to  do  the  same  class  of  work  exactly, 
there  is  practically  very  little  difference  between  the  completion  of  a 
local  call  and  a  junction  call. 

Vol.  82.  54 


Laws  Webb. 


834    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :    [April  30th. 

Mr.  The  question  of  handling  very  large  numbers  of  subscribers  has 

Laws  Webb,  j^^^  solved  in  New  York  a  good  deal  in  this  way,  that  a  large  number 
of  what  you  might  call  satellite  exchanges  have  sprung  up  owing  to  the 
use  by  subscribers  of  what  we  call  private  branch  exchanges,  the  private 
branch  exchange  simply  consisting  of  a  miniature  exchange — it  often 
grows  to  be  a  pretty  large  one — on  the  premises  of  the  subscriber. 
That  class  of  service  was  at  first  introduced  to  give  a  good  service  to 
very  busy  subscribers.  We  found  that  a  great  many  subscribers  were 
over-using  their  lines,  and  were  blocking  their  lines  entirely  to  the 
inward  calls.  We  persuaded  those  very  busy  firms  to  take  a  branch 
exchange  outfit  consisting  of  a  switchboard  connected  by  a  number  of 
trunks  to  the  nearest  exchange,  and  from  the  switchboard  were  extended 
instruments  to  the  different  departments  and  offices  of  the  people  who 
had  to  use  the  service.  A  trained  operator  was  put  at  the  switchboard, 
and  the  whole  service  of  that  subscriber  was  handled  through  that 
private  branch  switchboard.  At  first  it  was  pretty  difficult  to  get 
business  concerns  to  take  up  that  class  of  service  :  it  cost  ♦more,  and 
they  did  not  see  why  they  should  not  use  a  telephone  in  the  old  way, 
that  is,  working  one  flat  rate  line  so  that  it  was  used  almost  exclusively 
for  outward  calls  and  gave  the  inward  traffic  no  chance  at  all.  How- 
ever, that  private  exchange  system  gave  so  much  improved  a  service,  and 
handled  the  traffic  of  a  busy  subscriber  so  effectively,  that  it  very  soon 
became  popular,  and  now  instead  of  having  to  push  it  by  means  of 
canvassing,  and  so  on,  it  has  become  the  accepted  thing,  and  there  are 
actually  in  New  York  in  private  employ,  operating  branch  exchange 
switchboards,  about  twice  as  many  trained  operators  as  there  are  in 
the  main  telephone  exchanges  themselves.  There  are,  I  should  think, 
at  a  rough  guess — I  have  not  got  the  exact  figures  in  my  mind — approxi- 
mately 30,000  stations  out  of  100,000  stations  in  New  York  that  are 
operated  on  private  branch  exchanges.  That  method  of  working  the 
telephone  service  undoubtedly  largely  helps  us  to  solve  the  question  of 
dealing  with  very  large  numbers  of  subscribers.  Where  you  have  big 
establishments,  such  as  large  hotels  and  large  apartment  houses,  it 
gives  an  admirable  service,  and  it  of  course  largely  saves  in  the  number 
of  lines  required  to  serve  a  given  number  of  telephone  users.  It  is  the 
practice  now  in  New  York  to  build  no  large  apartment  house  or  large 
hotel  without  putting  in  a  private  branch  exchange  with  a  telephone  in 
every  apartment,  and  I  think,  in  fact,  the  New  York  Telephone  Company 
has  contracts  for  private  branch  exchanges  to  be  equipped  in  hotels 
that  are  not  even  yet  built,  so  thoroughly  is  the  use  of  the  telephone 
recognised  in  New  York. 
Mr.  Giu.  Mr.  Frank  Gill  :  Mr.  Aitken's  paper  is  somewhat  unusual  in  that, 

instead  of  propounding  a  definite  problem  of  known  factors,  he  gives  a 
somewhat  speculative  paper.  But  I  do  not  think  it  is  any  less  impor- 
tant on  that  account,  because  it  deals  with  a  very  large  and  difficult 
subject,  and  even  on  the  "  cheap  and  nasty  "  plan  his  115,000  subscribers 
involves  figures  running  into  some  millions.  I  should  like  to  congratu- 
late Mr.  Aitken  on  the  abiUty  he  has  shown  in  handling  his  subject. 
For  reasons  which  are  fairly  obvious  I  prefer  not  to  express  any  very 
strong  opinion  one  way  or  the  other,  but  I  desire  to  point  out  one  or 


1903.]     AN  EFFICIENT  TELEPHONE  SYSTEM:  DISCUSSION.       825 

two  things  which  should  be  borne  in  mind  by  teliephone  engineers  who   Mr.  Gui. 
contemplate  putting  in  a  divided  board.    In  the  first  place  I  understand 
there  are  only  two  divided  boards  in  existence,  one  in  St.  Louis  and 
one  in  Cleveland,  each  for  20,000  lines.   One  most  important  factor  which 
conies  in  is  time.     Every  telephone  subscriber  wants  to  get  through 
almost  before  he  makes  his  request,  and  I  doubt  very  much  whether 
there  is  anything  in  the  commercial  world  or  in  the  scientific  world 
which  is  cut  quite  so  fine  as  ordinary  telephone  operating.    The  first 
query  which  comes  is  this,  I  rather  want  to  apologise  to  the  Institution 
for  trying  to  introduce  a  new  factor  ;  we  have  such  a  lot  of  factors  that 
one  hesitates  to  bring  in  another  one,  namely,  the  time-factor.    The 
time-factor  of  a  subscriber's  line  is,  we  know,  roughly  about  2*28  per 
cent. ;  the  time-factor  of  a  junction  line — or,  as  they  call  it  in  New 
York,  a  trunk  line — is  about  23*5  per  cent.    That  immediately  raises 
the  very  important  fact  that,  if  you  are  going  to  extend  copper,  you 
extend  copper  which  will  be  used  in  one  ratio  or  in  the  other.     In 
Mr.  Aitken's  Fig.  i,  I  have  assumed,  taking  out  figures  as  far  as  I  could 
without  knowing  the  conditions  of  the  locality  in  which  the  exchange 
was  to  t>e  planted,  that  there  would  be  1 15,000  lines,  which  would  equal 
about  70,000  miles  of  metallic  circuit ;   there  would  be,  in  addition, 
about  60,000  miles  of  metallic  circuit  for  junctions.     In  Fig.  9,  I  make 
out  there  would  be  something  Hke  172,000  miles  of  metallic  circuit  for 
subscribers'  lines,  and  about  14,000  miles  for  junctions,  a  very  consider- 
able reduction.    The  difference,  therefore,  is  56,000  miles  of  metallic 
circuit  against   Fig.  9,  which   is  approximately  about   1,000  tons  of 
copper.      Perhaps  telephone  men  will  follow  the  point  a  little  easier 
if  I  say  183  miles  of  306  pair  cable.     It  is  a  serious  item,  which  you 
must  consider,  and  see  whether  what  you  get  is  worth  it.    On  the 
intermediate  distributing  board  there  would  be  three  divisions,  two 
of  them  extra.    There  would  be  probably  something  like  123  tons  more 
of  copper  on  those  two.    The  jumpers  for  the  two  divisions  would  be 
extra.    There  would  be  also  a  whole  lot  of  smaller  details.    The  inter- 
mediate boards  would  be  each  full  size,  and  the  main  frame  would  be 
larger.    The  line  lamps,  the  line  relays,  fitted  with  a  back  contact  in  a 
doubtful  situation,  would  be   more — I  am  sorry  Mr.  Swinburne  has 
gone,  because  I  wanted  to  tell  him  that  we  no  longer  wind  electro- 
magnets with  german-silver  wire,  if  indeed  it  was  ever  done — there 
would  be  also  the  keys  on  the  instruments.    Against  these  items — I 
have  not  noted  them  because  Mr.  Aitken  has  covered  them  very  fully — 
there  would  undoubtedly  be  a  large  number  of  savings.    Mr.  Webb  has 
rather  anticipated  me  in  regard  to  the  question  of  the  ratio  of  junction 
calls.     In  the  paper  (page  814)  a  problem  is  worked  out  which  is  based 
on  the  ration  of  i  ;  2.     I  make  out  that  if  one  takes  the  ratio  as  i  :  1*3, 
instead  of  requiring  66  J  sections  one  will  only  require  51  f  sections. 
The  distribution  on  a  divided  board  is  much  more  difficult,  because  you 
have  to  distribute  each  section  of  the  intermediate  board  separately. 
In  calculating  the  average  numerical  chances  of  junction  working,  in 
Fig.  I  we  have  97  per  cent. — that  is,  the  chances  of  the  call  being  an 
outgoing  call — and  in  Fig.  9,  89  per  cent. ;  but,  of  course,  you  have  to 
consider  the  direction  of  the  traffic. 


Mr.  Gill. 


Mr. 
Harrison. 


826    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :     [April  80th, 

I  would  conclude  by  one  suggestion,  that  if ,  as  I  have  endeavoured 
to  show,  the  length  of  the  subscribers'  line  in  a  divided  board  system  is 
a  serious  item,  and  one  which  requires  to  be  considered  carefully,  then 
the  same  item  also  requires  grave  consideration  in  any  attempt  made  to 
bring  two  exchanges  together  in  one  building,  where  one  gets  all  the 
junction  work  and  none  of  the  advantages  of  the  divided  board. 

Mr.  H.  H.  Harrison  :  I  have  been  very  interested  in  the  paper 
which  has  been  read,  as  the  question  of  the  adoption  of  divided 
multiple  boards  interested  me  some  five  or  six  years  ago,  before 
Mr.  Kellogg  brought  out  his  important  patent.  Mr.  Aitken  seems  to 
have  assumed  that  we  all  know  the  necessity  for  divided  boards. 
Briefly,  it  is,  of  course,  that,  as  the  number  of  subscribers  goes  up, 
the  multiple  connections,  or  panel  area,  required  to  enable  the  operator 
to  communicate  with  any  subscriber  become  so  great  that  it  is  no 


longer  possible  for  one  operator  to  complete  the  connection.  Hence 
this  gave  rise  over  the  other  side  to  what  was  called,  I  believe,  the 
"express"  system.  That  consisted  of  two  boards — one  in  which  the 
calls  were  received,  and  the  other  board,  or  B  board,  as  it  was  called, 
in  which  the  connection  required  was  effected.  This,  in  turn,  neces- 
sitated call-wires  between  the  boards  and  two  operators  for  every 
connection  made.  The  divided  board  system,  as  described,  is  very 
ingeniously  worked  out,  but  I  think  it  might  be  found  rather  difficult 
in  practice.  For  instance,  it  is  pretty  certain  that  the  number  of 
divisions  would  have  to  be  limited  to  four,  because  with  an  ordinary 
metallic  loop  no  simple  system  of  selective  signalling  is  possible  in 
more  than  four  ways  ;  and  while  I  do  not  think  it  is  too  much  to  ask  a 
subscriber  to  select  one  of  four  buttons,  any  more  than  it  is  asking  too 
much  of  him  to  look  up  the  number  of  the  required  subscriber  in  his 
telephone  directory,  he  might  reply,  if  you  ask  him  to  make  combina- 
tions with  four  buttons — the  telephone  subscriber  is  rather  an  impolite 
person — that  he  was  not  having  any  ;  so  it  is  pretty  certain,  therefore, 
that  that  limits  the  number  of  divisions  to  four.  I  would  point  out 
that  the  excellence  of  Mr.  Aitken's  divided  board  service  might  be 
such  that  in  course  of  time  he  would  have  each  one  of  his  four  boards 


1903.]    AN  EFFICIENT  TELEPHONE  SYSTEM  :  DISCUSSION.      827 

beginning  to  grow  unwieldy,  as  the  early  multiple  boards  did,  and  then  Mr. 
he  would  be  in  the  same  difficulty  as  the  early  telephone  people  were.  "* 

I  therefore  want  to  describe  a  system  called  the  Duplex  Multiple 
Board,  which  was  invented  over  the  other  side,  I  believe,  one  exchange 
of  which  was  worked  on  the  system.  As  it  requires  a  diagram  to 
adequately  describe  it,  I  will  ask  your  permission  to  communicate  the 
rest  of  my  remarks. 

(Communicated.)  In  the  duplex  multiple  system  the  subscribers  are 
divided  into  two  groups,  A  and  B.  Each  line  terminates  in  a  local  jack 
in  the  usual  manner.  The  multiple  jacks  are  of  special  construction. 
They  consist,  as  shown  in  the  diagram.  Fig.  A,  of  two  pairs  of  line 
springs  to  which  the  A  and  B  lines  are  connected  respectively,  and 
the  bushes  are  split  to  form  the  necessary  testing  circuits. 

It  is  claimed  for  this  board  that  its  capacity  can  be  increased  to 
double  that  of  the  ordinary  type,  the  multiple  area  remaining  the  same. 
It  has,  however,  two  serious  disadvantages.  Three  plugs  are  required, 
an  ordinary  answering  plug  and  an  A  and  a  B  plug  ;  further,  care  is 
required  in  testing  for  the  engaged  signal  to  see  that  the  right  half  of 
the  bush  is  touched. 

It  is,  however,  an  interesting  attempt  to  reduce  the  number  of  the 
junction  lines  by  increasing  the  capacity  of  the  central  exchange  with- 
out, at  the  same  time,  requiring  a  system  of  selective  signalUng. 

Mr.  J.  E.  Kingsbury  :  I  should  rather  have  preferred,  sir,  that  Mr. 
somebody  having  more  confidence  in  Mr.  Aitken's  system  than  I  have  ^°&'*'"^- 
should  have  spoken  at  this  stage,  in  order  that  "he  might  have  had  some 
of  the  support  which  I  feel  he  deserves,  if  only  for  bringing  such  a 
paper  before  us.  We  have  lacked  telephone  papers,  and  are  therefore 
very  much  indebted  to  him  for  the  one  which  he  has  re^.  I  think, 
however,  there  is  some  danger  of  our  taking  his  paper  too  seriously. 
I  am  not  at  all  sure  that  Mr.  Aitken  has  not  brought  this  paper  before 
us  as  something  for  discussion,  rather  than  for  us  to  assume  that  he  is 
prepared  to  take  the  responsibility  of  the  adoption  of  the  system  he 
proposes  in  one  of  the  world's  capitals.  I  believe  the  system  has  not 
yet  been  put  into  operation.  It  is  something,  therefore,  of  an  experi- 
ment ;  and  one  of  the  world's  capitals  is  the  last  place  in  the  world 
where  any  responsiWe  telephone  engineer  would  think  of  trying 
experiments.  For  that  reason  I  think  we  need  not,  as  I  say,  con- 
sider it  altogether  too  seriously.  But  we  must  recognise  the  fact 
that  in  the  development  of  the  telephone  growth  which  must  come  we 
shall  need  all  the  invention  that  we  can  get,  and  it  is  even  possible  we 
may  have  to  call  upon  the  public  to  do  what  Mr.  Aitken  is  perfectly 
ready  to  allow  them  to  do.  But  before  we  do  that  I  feel  that  we  must 
exhaust  many  other  sources  of  invention  that  we  have  not  yet  touched. 
Let  us  consider  what  it  is  that  Mr.  Aitken  proposes.  He  proposes  that 
we  shall  have  a  series  of  switchboards,  on  each  of  which  a  portion  of 
the  jacks  shall  be  multipled.  We  can  get  a  better  mental  conception 
of  the  arrangement  if  we  assume  a  scries  of  boards  painted  difiEerent 
colours ;  we  will  call  them  red,  white,  and  blue.  Upon  each  of  them 
is  a  signal,  which  may  be  operated  at  the  will  of  the  subscriber  by 
pressing  a  selected  button ;  and  under  such  circumstances  we  should 


828    AITKEN  :  DIVIDED  MULTIPLE  SWITCHBOARDS  :    [April  80th, 


Mr. 
Kingsbury. 


Mr.  Gavey. 


naturally  make  the  buttons  a  series  of  similar  colours.  Press  a  red 
button  and  you  drop  a  signal  on  the  red  board,  and  so  on.  That  is 
what  is  called  "  selective  signalling."  We  had  such  a  system  in  con- 
nection with  the  "  ring  through  "  system,  adopted  by  Mr.  Poole  in  the 
early  days  at  Manchester.  There  was  one  kind  of  indicator  which 
would  drop  by  pressing  a  white  button,  and  another  kind  of  indicator, 
a  clearing  indicator,  which  would  drop  by  pressing  a  black  button. 
In  those  days  there  was  only  one  line,  but  both  poles  of  the  battery 
were  utilised,  one  by  the  white  button  and  the  other  by  the  black. 
On  the  introduction  of  the  magneto  there  was  a  somewhat  similar 
use  of  a  single  line,  by  sending  an  alternating  current  on  one  occasion 
and  a  commutated  current  on  another.  That  gave  us  an  oppor- 
tunity by  magneto  working  of  selecting  either  one  of  the  two  signals. 
The  introduction  of  metallic  circuit  working  and  central  battery 
working  gave  us  an  opportunity  of  four  choices,  and  really  there  is 
very  little  reason  why,  since  a  four  party  line  is  an  easy  thing  to 
operate,  a  four  area  system  should  not  be  utilised,  working  on  the 
common  battery.  Of  course  it  involves  a  large  quantity  of  abstruse 
diagrams  and  a  large  amount  of  technical  ability  to  work  them  out,  but 
in  essence  that  is  what  it  amounts  to.  Mr.  Aitken  has  gone  into  the 
question  of  comparative  costs.  I  do  not  propose  to  follow  that  in  any 
detail ;  it  has  already  been  done  by  other  speakers.  But  I  would  like 
to  emphasise  Mr.  Webb's  remarks  in  regard  to  the  operation  of  the 
system  by  the  public.  I  anticipate  that  Mr.  Aitken  will  consider  that 
his  reliability  on  the  public  is  not  so  misplaced  as  some  of  us  think. 
My  impression  is  that  a  telephone  engineer  regards  his  subscribers 
individually  as  not  only  men  of  very  great  sense  and  ability,  but  I  am 
not  at  all  sure  whether  he  does  not  consider  them  all  Senior  Wranglers. 
The  poHce  regard  the  individuals  of  society  as  most  law-abiding  people, 
but  they  have  a  method  of  dealing  with  crowds  which  leaves  the 
individual,  and  the  law-abiding  character  of  the  individual,  out  of 
account.  The  telephone  engineer,  in  dealing  with  the  public,  has  to 
adopt  a  similar  distinction  between  individuals  and  telephone  sub- 
scribers. It  is  perfectly  useless  for  us  to  depend  upon  a  member  of 
the  public — perhaps  an  impatient  man  of  business,  whose  telephone 
call  may  mean  thousands  of  pounds — to  press  ttie  right  button  or  do 
the  right  thing  at  all  unless  it  is  absolutely  the  most  simple  thing.  For 
that  reason  alone  I  think  Mr.  Aitken's  method  of  a  divided  board 
cannot  be  expected  to  be  put  into  operation  until,  as  I  say,  other 
methods  have  been  exhausted.  Why  does  Mr.  Aitken  suggest  the 
divided  board  ?  Mr.  Kellogg  suggested  it  probably  ten  years  ago. 
He  suggested  it  when  the  limitation  of  the  multiple  board  was  about 
6,000 ;  to-day  it  is  20,000,  to-morrow  it  will  be  30,000 ;  and  I  see  no 
reason  to  assume  that  we  should  regard  that  number  as  in  any  way 
within  reach  of  the  limit.  All  we  can  say  at  present  is  that  the  multiple 
board  has  grown  in  its  capacity  with  the  requirements  of  the  business. 
I  see  no  reason  at  all  why  we  should  assume  that  its  progress  has 
stopped,  and  I  think  we  may  take  it  that  in  that  direction  inventive 
ingenuity  would  be  well  displayed. 

Mr.  J.  Gavey  :  Sir,  I  think  Mr.  Aitken  has  placed  the  Institution 


1903.]     AN  EFFICIENT  TELEPHONE  SYSTEJI  :  DISCUSSION.     8fl9 

under  a  debt  of  gratitude  for  having  brought  this  very  important   Mr.Gavey. 
matter  before  it  to-night.    Many  of  the  speakers  who  have  preceded 
me  have  made  remarks  which  in  some  cases  have  anticipated  my  own. 
In  reference  to  certain  criticisms  I  should  like,  however,  to  say  that  we 
have  not  reached  anything  like  finality,  and  that  we  ought  to,  and  we 
do,  welcome  every  attempt  that  is  made,  or  every  suggestion  that  is 
brought  before  us,  with  a  view  of  improving  the  telephone  service  of 
the  country.    The  problem  which  is  ever  present  to  the  mind  of  the 
telephone  engineer  is  simply  this — to  place  the  subscribers  in  com- 
munication in  the  shortest  possible  interval  of  time,  with  a  due  regard 
to  a  reasonable  capital  expenditure,  and  by  the  employment  of  the 
fe^rest  possible  number  of  operators.     This  problem  has  been  ever 
before  them,  but  as  new  devices  have  been  introduced  which  appeared 
to  simplify  the  problem  the  difficulties  have  increased,  owing  to  the 
growth  of  the  population  and  the  growth  of  telephone  subscribers. 
As  the  last  speaker  said,  it  is  only  a  few  years  ago  when  the  multiple 
board  was  supposed  to  meet  the  requirements  of  a  given  locality  with 
a  capacity  of  6,000.    Now  a  multiple  board  of  15,000  is  actually  in 
existence.    A  20,000  board  is  designed,  and   that   is  still   far  from 
meeting  the  requirements  of  the  public  ;  and  if  anything  in  the  nature 
of  Mr.  Aitken's  proposal — which  certainly  is  an  honest  endeavour  to 
meet  the  difficulty — can  be  adopted,  then  I  say  he  is  conferring  a 
benefit   on  the  community  in   bringing   the  subject  forward.     The 
divided  multiple  boards  that  have  been  used  in  America  can  hardly  be 
said  to  bear  very  seriously  on  the  problem,  because  they  do  not  provide 
automatic  signalling — ^at  least  those  that  I  saw  did  not.    They  are  all 
the  old  type,  involving  ringing  up  and  ringing  off,  and  whatever  may 
be  said  for  or  again